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You can compare the deionized water vs distilled water, however, to mention that the distilled water is that the same as deionized water may be a mistake. The terms “distilled water” and “deionized water” are usually misunderstood. during this article, you'll notice the reason to grasp the variations and similarities of those 2 completely different water cleanup technologies.
 
DISTILLED WATER
 
The oldest technique for production of pure water is that the thermal technique or distillation – water evaporation from the surface and condensation. the premise of the method is that the transfer of water within the vapor section with its later condensation. the most downside of this technique is that the terribly high maintenance prices of the electricity required to convert the water into the steam. additionally, within the method of steam formation in conjunction with water molecules, alternative solutes will enter the steam in keeping with their volatility. Evaporation is achieved in varied ways: the vacuum on top of the water, heating, etc.
 
Let’s contemplate the distillation. What’s happening within the method of distillation? The water molecules have the boiling purpose of 100°C or 212° F. alternative substances have completely different boiling points. The substance that boils at a lower temperature evaporates initial. The boiling purpose of assorted impurities is higher, and, in theory, they're going to begin to evaporate, once the water has already cooked out. The substance that boils at a lower temperature evaporates initial. because of this distinction the water is separated.
 
As a result, in theory when the distillation the fully pure water is obtained. Actually, organic substances, that have the similar boiling purpose than that of water will supply the water. let's say if the water contains the oil drops they will be found additionally within the liquid. There area unit much no salts within the water, as a result of the salt boils at a far higher temperature. To eliminate the matter of organic substances, the water distillers have pre- and post water filters.
 
The absolute advantage of the water is that the complete absence of harmful substances.
 
REVERSE OSMOSIS (RO) WATER
 
The latest various to the thermal technique for getting of water may be a two-stage reverse diffusion. The technology relies on the double passage of raw water through a tissue layer beneath the pressure. As a result, water is split into 2 streams: the filtrate (purified water) and concentrate (a targeted resolution of impurities). The two-stage reverse diffusion system will considerably cut back operational prices and improve the standard of obtained water. The reverse diffusion water treatment technology is that the most typically employed in households and within the trade for preparation of drinkable.
 
DEIONIZED (DI) WATER
 
Deionized water is deeply demineralized, ultrapure water with the impedance on the point of eighteen megohm-cm. it's employed in electronics, computer circuit boards, instrument manufacture, pharmacy, laundry liquids, etc.
 
In order to get the top quality pure deionized water, a multi-stage water purification method is used. when pre-cleaning, the water is equipped with the reverse diffusion membrane, so the water is filtered through a special deionization medium, that removes the remainder of the ions from the water. The purity of deionized water will exceed the purity of water.
 
SIMILARITIES AND DIFFERENCES: DISTILLED WATER Vs RO WATER Vs  DEIONIZED WATER 
 
 DISTILLED WATER REVERSE OSMOSIS (RO) WATER DEIONIZED (DI) WATER
Distillation is employed in the main in laboratories and factories, wherever it's required. Reverse diffusion is widely employed in water treatment plants, each reception and for the manufacture of assorted drinks, drinking water, etc.
  • RO water is additional saturated with salts and atomic number 8 then the water and DI water.
  • Reverse osmosis and deionization are more cost-effective than the distillation.
DI water is as pure because the water or maybe purer

 

Distillation, RO and deionization processes are supposed to purify the water of the contaminants: mercury, lead, strontium, nitrates, phosphates, manganese, in addition, pesticides.
 
Diabetes is epidemic; there is barely any family left that does not have a member diagnosed with diabetes. In urban areas, almost one-tenth of people have diabetes, and at least one-third are at risk of developing it soon if they do not do something about it. That means if not diabetic, every family surely has someone with prediabetes.
 
Diabetes is primarily caused by faulty lifestyle, followed for years, wrong kind of diet, absolute lack of exercise, and chronic stress, and low interaction between family members are all contributors to it.
 
Diabetes differs from all the other diseases in a way that it is infectious by lifestyle instead of microbes. Meaning a particular kind of lifestyle seems to prevail within the family. Finding an only single obese person in a family is rare. Similarly, if one is not doing exercise in the family, probably none is doing it.
 
The family is intended to function as a single entity, but not in negative direction, thus by changing the course of lifestyle by motivating and helping each other, whole family can benefit.
 
However, it seems that families are not discussing much diabetes, exercise, stress, and emotional problems.
 
“They say they care, but they rarely help, participate or motivate, they do not seem to understand me” is the most common complaint of people about their family members and close friends. In fact, some research shows that often friends are helping and providing more emotional support than the family members.
 
Although we all expect greater emotional support from family members, lack of such support may have reasons like little time or other lifestyle issues.
 
Can family support indeed make a difference?
 
At least all the research, hundreds of them, seems to support the idea that family support can make a huge difference. As we already mentioned that particular kind of lifestyle is prevalent in the whole family.
 
Whether it is a preference for specific type of food items, going out, meeting friends, doing exercise, spending leisure time, everything needs to be changed in diabetes, and perhaps everyone in the family has to change a bit. Wouldn’t it be best to work as a team? Instead of individual efforts. Sharing experience, motivating, has indeed shown to make efforts more successful.
 
Research has shown that adherence to exercise and medications are much better when done with the family support. Married people usually have higher compliance rate, though that cannot always be said about the lifestyle changes. People with families may exercise less as compared to those living alone.
 
Isn’t a family all about emotional support, love, help? Principally it must be the case, though in reality things often differ.
 
Thus for better diabetes management, prevention, it is vital that the whole family participates, and the process does not have to be boring. Supporting each other should be converted into a game, a fun, something to be enjoyed, something that brings emotional happiness to all the participants.
 
Iron sharpens iron; humans are not made to be left alone. They always psychologically feel better when they are continually communicating, when they are loved and praised. Modern technology has made us busier than ever; we are spending more time in unnecessary communication at the cost of neglecting the necessary one.
 
Thus the solution to the problem created by the technology should also be sought in technological advancement itself.
 
Why not start using an app that is made explicitly for members of the family, instead of social apps that are more open, and less focused on interaction at the family level.
 
An app called CricleCare is explicitly made to fulfill that gap. It is a fun way to keep you close friends and family members motivated. It is different in a way that it has been created to improve the communication between the small and closed circles. It has all the tools to make that conversation more relaxed and fun. So you can exchange messages, send stickers. Most importantly, you can encourage the family members by giving batches. Thus you can provide batches to kids for being good at home, doing all the tasks. Give batches for keeping up with exercise, reminding to take medicine, and much more. It has many features of health app like counting steps, providing information about burnt calories. However, unlike the traditional health apps, it is also about the involvement of the whole family. It merges the benefits of health app and family support platform.
Total serum thyroxine includes both free and protein-bound thyroxine and is usually measured by competitive immunoassay. Normal level in adults is 5.0-12.0 μg/dl.
 
Test for total thyroxine or free thyroxine is usually combined with TSH measurement and together they give the best assessment of thyroid function.
 
Causes of Increased Total T4
 
  1. Hyperthyroidism: Elevation of both T4 and T3 values along with decrease of TSH are indicative of primary hyperthyroidism.
  2. Increased thyroxine-binding globulin: If concentration of TBG increases, free hormone level falls, release of TSH from pituitary is stimulated, and free hormone concentration is restored to normal. Reverse occurs if concentration of binding proteins falls. In either case, level of free hormones remains normal, while concentration of total hormone is altered. Therefore, estimation of only total T4 concentration can cause misinterpretation of results in situations that alter concentration of TBG.
  3. Factitious hyperthyroidism
  4. Pituitary TSH-secreting tumor.
 
Causes of Decreased Total T4
 
  1. Primary hypothyroidism: The combination of decreased T4 and elevated TSH are indicative of primary hypothyroidism.
  2. Secondary or pituitary hypothyroidism
  3. Tertiary or hypothalamic hypothyroidism
  4. Hypoproteinaemia, e.g. nephrotic syndrome
  5. Drugs: oestrogen, danazol
  6. Severe non-thyroidal illness.
 
Free Thyroxine (FT4)
 
FT4 comprises of only a small fraction of total T4, is unbound to proteins, and is the metabolically active form of the hormone. It constitutes about 0.05% of total T4. Normal range is 0.7 to 1.9 ng/dl. Free hormone concentrations (FT4 and FT3) correlate better with metabolic state than total hormone levels (since they are not affected by changes in TBG concentrations).
 
Measurement of FT4 is helpful in those situations in which total T4 level is likely to be altered due to alteration in TBG level (e.g. pregnancy, oral contraceptives, nephrotic syndrome).
 
Total and Free Triiodothyronine (T3)
 
Uses
 
  1. Diagnosis of T3 thyrotoxicosis: Hyperthyroidism with low TSH and elevated T3, and normal T4/FT4 is termed T3 thyrotoxicosis.
  2. Early diagnosis of hyperthyroidism: In early stage of hyperthyroidism, total T4 and free T4 levels are normal, but T3 is elevated.
 
A low T3 level is not useful for diagnosis of hypothyroidism since it is observed in about 25% of normal individuals.
 
For routine assessment of thyroid function, TSH and T4 are measured. T3 is not routinely estimated because normal plasma levels are very low.
 
Normal T3 level is 80-180 ng/dl.
 
Free T3: Measurement of free T3 gives true values in patients with altered serum protein levels (like pregnancy, intake of estrogens or oral contraceptives, and nephrotic syndrome). It represents 0.5% of total T3.
 
Thyrotropin Releasing Hormone (TRH) Stimulation Test
 
Uses
 
  1. Confirmation of diagnosis of secondary hypothyroidism
  2. Evaluation of suspected hypothalamic disease
  3. Suspected hyperthyroidism
 
This test is not much used nowadays due to the availability of sensitive TSH assays.
 
Procedure
 
  • A baseline blood sample is collected for estimation of basal serum TSH level.
  • TRH is injected intravenously (200 or 500 μg) followed by measurement of serum TSH at 20 and 60 minutes.
 
Interpretation
 
  1. Normal response: A rise of TSH > 2 mU/L at 20 minutes, and a small decline at 60 minutes.
  2. Exaggerated response: A further significant rise in already elevated TSH level at 20 minutes followed by a slight decrease at 60 minutes; occurs in primary hypothyroidism.
  3. Flat response: There is no response; occurs in secondary (pituitary) hypothyroidism.
  4. Delayed response: TSH is higher at 60 minutes as compared to its level at 20 minutes; seen in tertiary (hypothalamic) hypothyroidism.
 
Antithyroid Antibodies
 
Box 864.1 Thyroid autoantibodies
 
  • Useful for diagnosis and monitoring of autoimmune thyroid diseases.
  • Antimicrosomal or antithyroid peroxidase antibodies: Hashimoto’s thyroiditis
  • Anti-TSH receptor antibodies: Graves’ disease
Various autoantibodies (TSH receptor, antimicrosomal, and antithyroglobulin) are detected in thyroid disorders like Hashimoto’s thyroiditis and Graves’ disease. Antimicrosomal (also called as thyroid peroxidase) and anti-thyroglobulin antibodies are observed in almost all patients with Hashimoto’s disease. TSH receptor antibodies (TRAb) are mainly tested in Graves’ disease to predict the outcome after treatment (Box 864.1).
 
Radioactive Iodine Uptake (RAIU) Test
 
This is a direct test that assesses the trapping of iodide by thyroid gland (through the iodine symporters or pumps in follicular cells) for thyroid hormone synthesis. Patient is administered a tracer dose of radioactive iodine (131I or 123I) orally. This is followed by measurement of amount of radioactivity over the thyroid gland at 2 to 6 hours and again at 24 hours. RAIU correlates directly with the functional activity of the thyroid gland. Normal RAIU is about 10-30% of administered dose at 24 hours, but varies according to the geographic location due to differences in dietary intake.
 
Causes of Increased Uptake
 
  • Hyperthyroidism due to Graves’ disease, toxic multinodular goiter, toxic adenoma, TSH-secreting tumor.
 
Causes of Decreased Uptake
 
  • Hyperthyroidism due to administration of thyroid hormone, factitious hyperthyroidism, subacute thyroiditis.
 
Uses
 
RAIU is most helpful in differential diagnosis of hyperthyroidism by separating causes into those due to increased uptake and due to decreased uptake.
 
Thyroid Scintiscanning
 
An isotope (99mTc-pertechnetate) is administered and a gamma counter assesses its distribution within the thyroid gland.
 
Interpretation
 
  • Differential diagnosis of high RAIU thyrotoxicosis:
    – Graves’ disease: Uniform or diffuse increase in uptake
    – Toxic multinodular goiter: Multiple discrete areas of increased uptake
    – Adenoma: Single area of increased uptake
  • Evaluation of a solitary thyroid nodule:
    – ‘Hot’ nodule: Hyperfunctioning
    – ‘Cold’ nodule: Non-functioning; about 20% cases are malignant.
 
Interpretation of thyroid function tests is shown in Table 164.1.
 
Table 864.1 Interpretation of thyroid function tests
Test results Interpretations
1. TSH Normal, FT4 Normal Euthyroid
2. Low TSH, Low FT4 Secondary hypothyroidism
3. High TSH, Normal FT4 Subclinical hypothyroidism
4. High TSH, Low FT4 Primary hypothyroidism
5. Low TSH, Normal FT4, Normal FT3 Subclinical hyperthyroidism
6. Low TSH, Normal FT4, High FT3 T3 toxicosis
7. Low TSH, High FT4 Primary hyperthyroidism
 
Neonatal Screening for Hypothyroidism
 
Thyroid hormone deficiency during neonatal period can cause severe mental retardation (cretinism) that can be prevented by early detection and treatment. Estimation of TSH is done on dry blood spots on filter paper or cord serum between 3rd to 5th days of life. Elevated TSH is diagnostic of hypothyroidism. In infants with confirmed hypothyroidism, RAIU (123I) scan should be done to distinguish between thyroid agenesis and dyshormonogenesis.
Box 863.1 Terminology in thyroid disorders
  • Primary hyper-/hypothyroidism: Increased or decreased function of thyroid gland due to disease of thyroid itself and not due to increased or decreased levels of TRH or TSH.
  • Secondary hyper-/hypothyroidism: Increased or decreased function of thyroid gland due to increased or decreased levels of TSH.
  • Tertiary hypothyroidism: Decreased function of thyroid gland due to decreased function of hypothalamus.
  • Subclinical thyroid disease: A condition with abnormality of thyroid hormone levels in blood but without specific clinical manifestations of thyroid disease and without any history of thyroid dysfunction or therapy.
  • Subclinical hyperthyroidism: A condition with normal thyroid hormone levels but with low or undetectable TSH level.
  • Subclinical hypothyroidism: A condition with normal thyroxine and triiodothyronine level along with mildly elevated TSH level.
Among the endocrine disorders, disorders of thyroid are common and are only next in frequency to diabetes mellitus. They are more common in women than in men. Functional thyroid disorders can be divided into two types depending on activity of the thyroid gland: hypothyroidism (low thyroid hormones), and hyperthyroidism (excess thyroid hormones). Any enlargement of thyroid gland is called as a goiter. Terminology related to thyroid disorders is shown in Box 863.1.
 
Hyperthyroidism
 
Hyperthyroidism is a condition caused by excessive secretion of thyroid hormone. Causes of hyperthyroidism are listed in Table 863.1.
 
Table 863.1 Causes of hyperthyroidism
  1. Graves’ disease (Diffuse toxic goiter)
  2. Toxicity in multinodular goiter
  3. Toxicity in adenoma
  4. Subacute thyroiditis
  5. TSH-secreting pituitary adenoma (secondary hyperthyroidism)
  6. Trophoblastic tumours that secrete TSH-like hormone: choriocarcinoma, hydatidiform mole
  7. Factitious hyperthyroidism
 
Clinical Characteristics
 
Clinical characteristics of hyperthyroidism are nervousness, anxiety, irritability, insomnia, fine tremors; weight loss despite normal or increased appetite; heat intolerance; increased sweating; dyspnea on exertion; amenorrhea and infertility; palpitations, tachycardia, cardiac arrhythmias, heart failure (especially in elderly); and muscle weakness, proximal myopathy, and osteoporosis (especially in elderly).
 
The triad of Graves’ disease consists of hyperthyroidism, ophthalmopathy (exophthalmos, lid retraction, lid lag, corneal ulceration, impaired eye muscle function), and dermopathy (pretibial myxoedema).
 
Box 863.2 Thyroid function tests in hyperthyroidism
  • Thyrotoxicosis:
    Serum TSH low or undetectable
    – Raised total T4 and free T4.
  • T3 toxicosis:
    – Serum TSH undetectable
    – Normal total T4 and free T4
    – Raised T3
Laboratory Features
 
In most patients, free serum T3 and T4 are elevated. In T3 thyrotoxicosis (5% cases of thyrotoxicosis), serum T4 levels are normal while T3 is elevated. Serum TSH is low or undetectable (< 0.1 mU/L) (Box 863.2).
 
Undetectable or low serum TSH along with normal levels of T3 and T4 is called as subclinical hyperthyroidism; subtle signs and symptoms of thyrotoxicosis may or may not be present. Subclinical hyperthyroidism is associated with risk of atrial fibrillation, osteoporosis, and progression to overt thyroid disease.
 
Features of primary and secondary hyperthyroidism are compared in Table 863.2.
 
Table 863.2 Differences between primary and secondary hyperthyroidism
Parameter Primary hyperthyroidism Secondary hyperthyroidism
1. Serum TSH Low Normal or high
2. Serum free thyroxine High High
3. TSH receptor antibodies May be positive Negative
4. Causes Graves’ disease, toxic multinodular goiter, toxic adenoma Pituitary adenoma
 
Evaluation of hyperthyroidism is presented in Figure 863.1.
 
Figure 863.1 Evaluation of hyperthyroidism
Figure 863.1 Evaluation of hyperthyroidism. TSH: thyroid stimulating hormone; FT4: free T4; FT3: free T3; TRAb: TSH receptor antibody; TRH: Thyrotropin releasing hormone
 
Hypothyroidism
 
Hypothyroidism is a condition caused by deficiency of thyroid hormones. Causes of hypothyroidism are listed in Table 863.3. Primary hypothyroidism results from deficient thyroid hormone biosynthesis that is not due to disorders of hypothalamus or pituitary. Secondary hypothyroidism results from deficient secretion of TSH from pituitary. Deficient or loss of secretion of thyro-tropin releasing hormone from hypothalamus results in tertiary hypothyroidism. Secondary and tertiary hypothyroidism are much less common than primary. Plasma TSH is high in primary and low in secondary and tertiary hypothyroidism. Differences between primary and secondary hypothyroidism are shown in Table 863.4.
 
Table 863.3 Causes of hypothyroidism 
  1. Primary hypothyroidism (Increased TSH)
    • Iodine deficiency
    • Hashimoto’s thyroiditis
    Exogenous goitrogens
    • Iatrogenic: surgery, drugs, radiation
  2. Secondary hypothyroidism (Low TSH): Diseases of pituitary
  3. Tertiary hypothyroidism (Low TSH, Low TRH): Diseases of hypothalamus
 
Table 863.4 Differences between primary and secondary hypothyroidism
Parameter Primary hypothyroidism Secondary hypothyroidism
1. Cause Hashimoto’s thyroiditis Pituitary disease
2. Serum TSH High Low
3. Thyrotropin releasing hormone stimulation test Exaggerated response No response
4. Antimicrosomal antibodies Present Absent
 
Box 863.3 Thyroid function tests in hypothyroidism
  • Primary hypothyroidism
    – Serum TSH: Increased (proportional to degree of hypofunction)
    – Free T4: Decreased
    – TRH stimulation test: Exaggerated response
  • Secondary hypothyroidism
    – Serum TSH: Decreased
    – Free T4: Decreased
    – TRH stimulation test: Absent response
  • Tertiary hypothyroidism
    – Serum TSH: Decreased
    – FT4: Decreased
    – TRH stimulation test: Delayed response
Clinical features of primary hypothyroidism are: lethargy, mild depression, disturbances in menstruation, weight gain, cold intolerance, dry skin, myopathy, constipation, and firm and lobulated thyroid gland (in Hashimoto’s thyroiditis).
 
In severe cases, myxoedema coma (an advanced stage with stupor, hypoventilation, and hypothermia) can occur.
 
Laboratory Features
 
Laboratory features in hypothyroidism are shown in Box 863.3.
 
Normal serum thyroxine (T4 and FT4) coupled with a moderately raised TSH (>10 mU/L) is referred to as subclinical hypothyroidism. It is associated with bad obstetrical outcome, poor cognitive development in children, and high risk of hypercholesterolemia and progression to overt hypothyroidism.
 
Evaluation of hypothyroidism is presented in Figure 863.2
 
Figure 863.2 Evaluation of hypothyroidism
Figure 863.2 Evaluation of hypothyroidism. TSH: thyroid stimulating hormone; FT4: free T4; TRH: Thyrotropin releasing hormone
The ovaries are the sites of production of female gametes or ova by the process of oogenesis. The ova are released by the process of ovulation in a cyclical manner at regular intervals. Ovary contains numerous follicles that contain ova in various stages of development. During each menstrual cycle, up to 20 primordial follicles are activated for maturation; however, only one follicle becomes fully mature; this dominant follicle ruptures to release the secondary oocyte from the ovary. Maturation of the follicle is stimulated by follicle stimulating hormone (FSH) secreted by anterior pituitary (Figure 862.1). Maturing follicle secretes estrogen that causes proliferation of endometrium of the uterus (proliferative phase). Follicular cells also secrete inhibin which regulates release of FSH by the anterior pituitary. Fall in FSH level is followed by secretion of luteinizing hormone (LH) by the anterior pituitary (LH surge). This causes follicle to rupture and the ovum is expelled into the peritoneal cavity near the fimbrial end of the fallopian tube. The fallopian tubes conduct ova from the ovaries to the uterus. Fertilization of ovum by the sperm occurs in the fallopian tube.
 
Figure 862.1 The hypothalamus pituitary ovarian axis
Figure 862.1 The hypothalamus-pituitary-ovarian axis 
 
The ovum consists of the secondary oocyte, zona pellucida and corona radiata. The ruptured follicle in the ovary collapses and fills with blood clot (corpus luteum). LH converts granulose cells in the follicle to lutein cells which begin to secrete progesterone. Progesterone stimulates secretion from the endometrial glands (secretory phase) that were earlier under the influence of estrogen. Rising progesterone levels inhibit LH production from the anterior pituitary. Without LH, the corpus luteum regresses and becomes functionless corpus albicans. After regression of corpus luteum, production of estrogen and progesterone stops and endometrium collapses, causing onset of menstruation. If the ovum is fertilized and implanted in the uterine wall, human chorionic gonadotropin (hCG) is secreted by the developing placenta into the maternal circulation. Human chorionic gonadotropin maintains the corpus luteum for secetion of estrogen and progesterone till 12th week of pregnancy. After 12th week, corpus luteum regresses to corpus albicans and the function of synthesis of estrogen and progesterone is taken over by placenta till parturition.
 
The average duration of the normal menstrual cycle is 28 days. Ovulation occurs around 14th day of the cycle. The time interval between ovulation and menstruation is called as luteal phase and is fairly constant (14 days) (Figure 862.2).
 
Figure 862.2 Normal menstrual cycle
Figure 862.2 Normal menstrual cycle
 
Causes of Female Infertility
 
Causes of female infertility are shown in Table 862.1.
 
Table 862.1 Causes of female infertility
1. Hypothalamic-pituitary dysfunction:
  • Hypothalamic causes
    – Excessive exercise
    – Excess stress
    – Low weight
    – Kallman’s syndrome
    Idiopathic
  • Pituitary causes
    – Hyperprolactinemia
    Hypopituitarism (Sheehan’s syndrome, Simmond’s disease)
    – Craniopharyngioma
    – Cerebral irradiation
 2. Ovarian dysfunction:
  • Polycystic ovarian disease (Stein-Leventhal syndrome)
  • Luteinized unruptured follicle
  • Turner’s syndrome
  • Radiation or chemotherapy
  • Surgical removal of ovaries
  • Idiopathic
 3. Dysfunction in passages:
  • Fallopian tubes
    Infections: Tuberculosis, gonorrhea, Chlamydia
    – Previous surgery (e.g. laparotomy)
    – Tubectomy
    Congenital hypoplasia, non-canalization
    Endometriosis
  • Uterus
    – Uterine malformations
    – Asherman’s syndrome
    – Tuberculous endometritis
    Fibroid
  • Cervix: Sperm antibodies
  • Vagina: Septum
 4. Dysfunction of sexual act: Dyspareunia
 
Investigations
 
Evaluation of female infertility is shown in Figure 862.3.
 
Figure 862.3 Evaluation of female infertility
Figure 862.3 Evaluation of female infertility. FSH: Follicle stimulating hormone; LH: Luteinizing hormone; DHEA-S: Dihydroepiandrosterone; TSH: Thyroid stimulating hormone; ↑ : Increased; ↓ : Decreased
 
Tests for Ovulation
 
Most common cause of female infertility is anovulation.
 
  1. Regular cycles, mastalgia, and laparoscopic direct visualization of corpus luteum indicate ovulatory cycles. Anovulatory cycles are clinically characterized by amenorrhea, oligomenorrhea, or irregular menstruation. However, apparently regular cycles may be associated with anovulation.
  2. Endometrial biopsy: Endometrial biopsy is done during premenstrual period (21st-23rd day of the cycle). The secretory endometrium during the later half of the cycle is an evidence of ovulation.
  3. Ultrasonography (USG): Serial ultrasonography is done from 10th day of the cycle and the size of the dominant follicle is measured. Size >18 mm is indicative of imminent ovulation. Collapse of the follicle with presence of few ml of fluid in the pouch of Douglas is suggestive of ovulation. USG also is helpful for treatment (i.e. timing of coitus or of intrauterine insemination) and diagnosis of luteinized unruptured follicle (absence of collapse of dominant follicle). Transvaginal USG is more sensitive than abdominal USG.
  4. Basal body temperature (BBT): Patient takes her oral temperature at the same time every morning before arising. BBT falls by about 0.5°F at the time of ovulation. During the second (progestational) half of the cycle, temperature is slightly raised above the preovulatory level (rise of 0.5° to 1°F). This is due to the slight pyrogenic action of progesterone and is therefore presumptive evidence of functional corpus luteum.
  5. Cervical mucus study:
    Fern test: During estrogenic phase, a characteristic pattern of fern formation is seen when cervical mucus is spread on a glass slide (Figure 862.4). This ferning disappears after the 21st day of the cycle. If previously observed, its disappearance is presumptive evidence of corpus luteum activity.
    Spinnbarkeit test: Cervical mucus is elastic and withstands stretching upto a distance of over 10 cm. This phenomenon is called Spinnbarkeit or the thread test for the estrogen activity. During the secretory phase, viscosity of the cervical mucus increases and it gets fractured when stretched. This change in cervical mucus is evidence of ovulation.
  6. Vaginal cytology: Karyopyknotic index (KI) is high during estrogenic phase, while it becomes low in secretory phase. This refers to percentage of super-ficial squamous cells with pyknotic nuclei to all mature squamous cells in a lateral vaginal wall smear. Usually minimum of 300 cells are evaluated. The peak KI usually corresponds with time of ovulation and may reach upto 50 to 85.
  7. Estimation of progesterone in mid-luteal phase (day 21 or 7 days before expected menstruation): Progesterone level > 10 nmol/L is a reliable evidence of ovulation if cycles are regular (Figure 862.5). A mistimed sample is a common cause of abnormal result.
 
Figure 862.4 Ferning of cervical mucosa
Figure 862.4 Ferning of cervical mucosa
 
Figure 862.5 Serum progesterone during normal menstrual cycle
Figure 862.5 Serum progesterone during normal menstrual cycle
 
Tests to Determine the Cause of Anovulation
 
  1. Measurement of LH, FSH, and estradiol during days 2 to 6: All values are low in hypogonadotropic hypogonadism (hypothalamic or pituitary failure).
  2. Measurement of TSH, prolactin, and testosterone if cycles are irregular or absent:
    Increased TSH: Hypothyroidism
    Increased prolactin: Pituitary adenoma
    Increased testosterone: Polycystic ovarian disease (PCOD), congenital adrenal hyperplasia (To differentiate PCOD from congenital adrenal hyperplasia, ultrasound and estimation of dihydroepiandrosterone or DHEA are done).
  3. Transvaginal ultrasonography: This is done for detection of PCOD.
 
Investigations to Assess Tubal and Uterine Status
 
  1. Infectious disease: These tests include endometrial biopsy for tuberculosis and test for chlamydial IgG antibodies for tubal factor in infertility.
  2. Hysterosalpingography (HSG): HSG is a radiological contrast study for investigation of the shape of the uterine cavity and for blockage of fallopian tubes (Figure 862.6). A catheter is introduced into the cervical canal and a radiocontrast dye is injected into the uterine cavity. A real time X-ray imaging is carried out to observe the flow of the dye into the uterine cavity, tubes, and spillage into the uterine cavity.
  3. Hysterosalpingo-contrast sonography: A catheter is introduced into the cervical canal and an echocontrast fluid is introduced into the uterine cavity. Shape of the uterine cavity, filling of fallopian tubes, and spillage of contrast fluid are noted. In addition, ultrasound scan of the pelvis provides information about any fibroids or polycystic ovarian disease.
  4. Laparoscopy and dye hydrotubation test with hysteroscopy: In this test, a cannula is inserted into the cervix and methylene blue dye is introduced into the uterine cavity. If tubes are patent, spillage of the dye is observed from the ends of both tubes. This technique also allows visualization of pelvic organs, endometriosis, and pelvic adhesions. If required, endometriosis and tubal blockage can be treated during the procedure.
 
Possible pregnancy and active pelvic or vaginal infection are contraindications to tubal patency tests.
 
Figure 862.6 Hysterosalpingography
Figure 862.6 Hysterosalpingography
The male reproductive system consists of testes (paired organs located in the scrotal sac that produce spermatozoa and secrete testosterone), a paired system of ducts comprising of epididymis, vasa deferentia, and ejaculatory ducts (collect, store, and conduct spermatozoa), paired seminal vesicles and a single prostate gland (produce nutritive and lubricating seminal fluid), bulbourethral glands of Cowper (secrete lubricating mucus), and penis (organ of copulation).
 
The hypothalamus secretes gonadotropin releasing hormone (GnRH) that regulates the secretion of the two gonadotropins from the anterior pituitary: luteinizing hormone (LH) and follicle stimulating hormone (FSH) (Figure 861.1). Luteinizing hormone primarily stimulates the production and secretion of testosterone from Leydig cells located in the interstitial tissue of the testes. Testosterone stimulates spermatogenesis, and plays a role in the development of secondary sexual characters. Testosterone needs to be converted to an important steroidal metabolite, dihydrotestosterone within cells to perform most of its androgenic functions. Testosterone inhibits LH secretion by negative feedback. Follicle stimulating hormone acts on Sertoli cells of seminiferous tubules to regulate the normal maturation of the sperms. Sertoli cells produce inhibin that controls FSH secretion by negative feedback.
 
Figure 861.1 Hypothalamus-pituitary-testis axis. + indicates stimulation; – indicates negative feedback
Figure 861.1 Hypothalamus-pituitary-testis axis. + indicates stimulation; – indicates negative feedback
 
During sexual intercourse, semen is deposited into the vagina. Liquefaction of semen occurs within 20-30 minutes due to proteolytic enzymes of prostatic fluid. For fertilization to occur in vivo, the sperm must undergo capacitation and acrosome reaction. Capacitation refers to physiologic changes in sperms that occur during their passage through the cervix of the female genital tract. With capacitation, the sperm acquires (i) ability to undergo acrosome reaction, (ii) ability to bind to zona pellucida, and (iii) hypermotility. Sperm then travels through the cervix and uterus up to the fallopian tube. Binding of sperm to zona pellucida induces acrosomal reaction (breakdown of outer plasma membrane by enzymes of acrosome and its fusion with outer acrosomal membrane, i.e. loss of acrosome). This is necessary for fusion of sperm and oocyte membranes. Acrosomal reaction and binding of sperm and ovum surface proteins is followed by penetration of zona pellucida of ovum by the sperm. Following penetration by sperm, hardening of zona pellucida occurs that inhibits penetration by additional sperms. A sperm penetrates and fertilizes the egg in the ampullary portion of the fallopian tube (Figure 861.2).
 
Figure 861.2 Steps before and after fertilization of ovum
Figure 861.2 Steps before and after fertilization of ovum
 
Causes of Male Infertility
 
Causes of male infertility are listed in Table 861.1.
 
Table 861.1 Causes of male infertility 
2. Hypothalamic-pituitary dysfunction (hypogonadotropic hypogonadism)
3. Testicular dysfunction:
  • Radiation, cytotoxic drugs, antihypertensives, antidepressants
  • General factors like stress, emotional factors, drugs like marijuana, anabolic steroids, and cocaine, alcoholism, heavy smoking, undernutrition
  • Mumps orchitis after puberty
  • Varicocele (dilatation of pampiniform plexus of scrotal veins)
  • Undescended testes (cryptorchidism)
  • Endocrine disorders like diabetes mellitus, thyroid dysfunction
  • Genetic disorders: Klinefelter’s syndrome, microdeletions in Y chromosome, autosomal Robertsonian translocation, immotile cilia syndrome (Kartagener’s syndrome), cystic fibrosis, androgen receptor gene defect
4. Dysfunction of passages and accessory sex glands:
 5. Dysfunction of sexual act:
  • Defects in ejaculation: retrograde (semen is pumped backwards in to the bladder), premature, or absent
  • Hypospadias
 
Investigations of Male Infertility
 
  1. History: This includes type of lifestyle (heavy smoking, alcoholism), sexual practice, erectile dysfunction, ejaculation, sexually transmitted diseases, surgery in genital area, drugs, and any systemic illness.
  2. Physical examination: Examination of reproductive system should includes testicular size, undescended testes, hypospadias, scrotal abnormalities (like varicocele), body hair, and facial hair. Varicocele can occur bilaterally and is the most common surgically removable abnormality causing male infertility.
  3. Semen analysis: See article Semen Analysis. Evaluation of azoospermia is shown in Figure 861.3. Evaluation of low semen volume is shown in Figure 861.4.
  4. Chromosomal analysis: This can reveal Klinefelter’s syndrome (e.g. XXY karyotype) (Figure 861.5), deletion in Y chromosome, and autosomal Robertsonian translocation. It is necessary to screen for cystic fibrosis carrier state if bilateral congenital absence of vas deferens is present.
  5. Hormonal studies: This includes measurement of FSH, LH, and testosterone to detect hormonal abnormalities causing testicular failure (Table 861.2).
  6. Testicular biopsy: Testicular biopsy is indicated when differentiation between obstructive and non-obstructive azoospermia is not evident (i.e. normal FSH and normal testicular volume).
 
Table 861.2 Interpretation of hormonal studies in male infertility 
Follicle stimulating hormone Luteinizing hormone Testosterone Interpretation
Low Low Low Hypogonadotropic hypogonadism (Hypothalamic or pituitary disorder)
High High Low Hypergonadotropic hypogonadism (Testicular disorder)
Normal Normal Normal Obstruction of passages, dysfunction of accessory glands
 
Figure 861.3 Evaluation of azoospermia
Figure 861.3 Evaluation of azoospermia. FSH: Follicle stimulating hormone; LH: Luteinizing hormone
 
Figure 861.4 Evaluation of low semen volume
Figure 861.4 Evaluation of low semen volume
 
Figure 861.5 Karyotype in Klinefelter's Syndrome
 Figure 861.5 Karyotype in Klinefelter’s syndrome (47, XXY)
 
Common initial investigations for diagnosis of cause of infertility are listed below.
 
Anatomically, stomach is divided into four parts: cardia, fundus, body, and pyloric part. Cardia is the upper part surrounding the entrance of the esophagus and is lined by the mucus-secreting epithelium. The epithelium of the fundus and the body of the stomach is composed of different cell types including: (i) mucus-secreting cells which protect gastric mucosa from self-digestion by forming an overlying thick layer of mucus, (ii) parietal cells which secrete hydrochloric acid and intrinsic factor, and (iii) peptic cells or chief cells which secrete the proteolytic enzyme pepsinogen. Pyloric part is divided into pyloric antrum and pyloric canal. It is lined by mucus-secreting cells and gastrin-secreting neuroendocrine cells (G cells) (Figure 859.1).
 
Figure 859.1 Parts of stomach and their lining cells
Figure 859.1 Parts of stomach and their lining cells 
 
In the stomach, ingested food is mechanically and chemically broken down to form semi-digested liquid called chyme. Following relaxation of pyloric sphincter, chyme passes into the duodenum.
 
There are three phases of gastric acid secretion: cephalic, gastric, and intestinal.
 
  • Cephalic or neurogenic phase: This phase is initiated by the sight, smell, taste, or thought of food that causes stimulation of vagal nuclei in the brain. Vagus nerve directly stimulates parietal cells to secrete acid; in addition, it also stimulates antral G cells to secrete gastrin in blood (which is also a potent stimulus for gastric acid secretion) (Figure 859.2). Cephalic phase is abolished by vagotomy.
  • Gastric phase: Entry of swallowed food into the stomach causes gastric distension and induces gastric phase. Distension of antrum and increase in pH due to neutralization of acid by food stimulate antral G cells to secrete gastrin into the circulation. Gastrin, in turn, causes release of hydrochloric acid from parietal cells.
  • Intestinal phase: Entry of digested proteins into the duodenum causes an increase in acid output from the stomach. It is thought that certain hormones and absorbed amino acids stimulate parietal cells to secrete acid.
 
The secretion from the stomach is called as gastric juice. The chief constituents of the gastric juice are:
 
  • Hydrochloric acid (HCl): This is secreted by the parietal cells of the fundus and the body of the stomach. HCl provides the high acidic pH necessary for activation of pepsinogen to pepsin. Gastric acid secretion is stimulated by histamine, acetylcholine, and gastrin (Figure 859.2). HCl kills most microorganisms entering the stomach and also denatures proteins (breaks hydrogen bonds making polypeptide chains to unfold). Its secretion is inhibited by somatostatin (secreted by D cells in pancreas and by mucosa of intestine), gastric inhibitory peptide (secreted by K cells in duodenum and jejunum), prostaglandin, and secretin (secreted by S cells in duodenum).
  • Pepsin: Pepsin is secreted by chief cells in stomach. Pepsin causes partial digestion of proteins leading to the formation of large polypeptide molecules (optimal function at pH 1.0 to 3.0). Its secretion is enhanced by vagal stimulation.
  • Mucus
  • Intrinsic factor (IF): IF is necessary for absorption of vitamin B12 in the terminal ileum. It is secreted by parietal cells of stomach.
 
Figure 859.2 Stimulation of gastric acid secretion
Figure 859.2 Stimulation of gastric acid secretion. Three receptors on parietal cells stimulate acid secretion: histamine (H2) receptor, acetylcholine or cholinergic receptor, and gastrin/CCK-B receptor. Histamine is released by enterochromaffin-like cells in lamina propria. Acetylcholine is released from nerve endings. Gastrin is released from G cells in antrum (in response to amino acids in food, antral distention, and gastrin-releasing peptide). After binding to receptors, H+ is secreted in exchange for K+ by proton pump
  • Gastric intubation for gastric analysis is contraindicated in esophageal stricture or varices, active nasopharyngeal disease, diverticula, malignancy, recent history of severe gastric hemorrhage, hypertension, aortic aneurysm, cardiac arrhythmias, congestive cardiac failure, or non-cooperative patient.
  • Pyloric stenosis: Obstruction of gastric outlet can elevate gastric acid output due to raised gastrin (following antral distension).
  • Pentagastrin stimulation is contraindicated in cases with allergy to pentagastrin, and recent severe gastric hemorrhge due to peptic ulcer disease.
 
Gastric analysis is not a commonly performed procedure because of following reasons:
 
  • It is an invasive and cumbersome technique that is traumatic and unpleasant for the patient.
  • Information obtained is not diagnostic in itself.
  • Availability of better tests for diagnosis such as endoscopy and radiology (for suspected peptic ulcer or malignancy); serum gastrin estimation (for ZE syndrome); vitamin assays, Schilling test, and antiparietal cell antibodies (for pernicious anemia); and tests for Helicobacter pylori infection (in duodenal or gastric ulcer).
  • Availability of better medical line of treatment that obviates need for surgery in many patients.
  1. Hollander’s test (Insulin hypoglycemia test): In the past, this test was used for confirmation of completeness of vagotomy (done for duodenal ulcer).

    Hypoglycemia is a potent stimulus for gastric acid secretion and is mediated by vagus nerve. This response is abolished by vagotomy.

    In this test, after determining BAO, insulin is administered intravenously (0.15-0.2 units/kg) and acid output is estimated every 15 minutes for 2 hours (8 post-stimulation samples). Vagotomy is considered as complete if, after insulin-induced hypoglycemia (blood glucose < 45 mg/dl), no acid output is observed within 45 minutres.

    The test gives reliable results only if blood glucose level falls below 50 mg/dl at some time following insulin injection. It is best carried out after 3-6 months of vagotomy.

    The test is no longer recommended because of the risk associated with hypoglycemia. Myocardial infarction, shock, and death have also been reported.

  2. Fractional test meal: In the past, test meals (e.g. oat meal gruel, alcohol) were administered orally to stimulate gastric secretion and determine MAO or PAO. Currently, parenteral pentagastrin is the gastric stimulant of choice.

  3. Tubeless gastric analysis: This is an indirect and rapid method for determining output of free hydrochloric acid in gastric juice. In this test, a cationexchange resin tagged to a dye (azure A) is orally administered. In the stomach, the dye is displaced from the resin by the free hydrogen ions of the hydrochloric acid. The displaced azure A is absorbed in the small intestine, enters the bloodstream, and is excreted in urine. Urinary concentration of the dye is measured photometrically or by visual comparison with known color standards. The quantity of the dye excreted is proportional to the gastric acid output. However, if kidney or liver function is impaired, false results may be obtained. The test is no longer in use.

  4. Spot check of gastric pH: According to some investigators, spot determination of pH of fasting gastric juice (obtained by nasogastric intubation) can detect the presence of hypochlorhydria (if pH>5.0 in men or >7.0 in women).

  5. Congo red test during esophagogastroduodenoscopy: This test is done to determine the completeness of vagotomy. Congo red dye is sprayed into the stomach during esophagogastroduodenoscopy; if it turns red, it indicates presence of functional parietal cells in stomach with capacity of producing acid.
 
REFERENCE RANGES
 
  • Volume of gastric juice: 20-100 ml
  • Appearance: Clear
  • pH: 1.5 to 3.5
  • Basal acid output: Up to 5 mEq/hour
  • Peak acid output: 1 to 20 mEq/hour
  • Ratio of basal acid output to peak acid output: <0.20 or < 20%
In gastric analysis, amount of acid secreted by the stomach is determined on aspirated gastric juice sample. Gastric acid output is estimated before and after stimulation of parietal cells (i.e. basal and peak acid output). This test was introduced in the past mainly for the evaluation of peptic ulcer disease (to assess the need for operative intervention). However, diminishing frequency of peptic ulcer disease and availability of safe and effective medical treatment have markedly reduced the role of surgery.
 
  1. To determine the cause of recurrent peptic ulcer disease:
    To detect Zollinger-Ellison (ZE) syndrome: ZE syndrome is a rare disorder in which multiple mucosal ulcers develop in the stomach, duodenum, and upper jejunum due to gross hypersecretion of acid in the stomach. The cause of excess secretion of acid is a gastrin-producing tumor of pancreas. Gastric analysis is done to detect markedly increased basal and pentagastrinstimulated gastric acid output for diagnosis of ZE syndrome (and also to determine response to acidsuppressant therapy). However, a more sensitive and specific test for diagnosis of ZE syndrome is measurement of serum gastrin (fasting and secretin-stimulated).
    To decide about completeness of vagotomy following surgery for peptic ulcer disease: See Hollander’s test.
  2. To determine the cause of raised fasting serum gastrin level: Hypergastrinemia can occur in achlorhydria, Zollinger-Ellison syndrome, and antral G cell hyperplasia.
  3. To support the diagnosis of pernicious anemia (PA): Pernicious anemia is caused by defective absorption of vitamin B12 due to failure of synthesis of intrinsic factor secondary to gastric mucosal atrophy. There is also absence of hydrochloric acid in the gastric juice (achlorhydria). Gastric analysis is done for demonstration of achlorhydria if facilities for vitamin assays and Schilling’s test are not available (Achlorhydria by itself is insufficient for diagnosis of PA).
  4. To distinguish between benign and malignant ulcer: Hypersecretion of acid is a feature of duodenal peptic ulcer, while failure of acid secretion (achlorhydria) occurs in gastric carcinoma. However, anacidity occurs only in a small proportion of cases with advanced gastric cancer. Also, not all patients with duodenal ulcer show increased acid output.
  5. To measure the amount of acid secreted in a patient with symptoms of peptic ulcer dyspepsia but normal X-ray findings: Excess acid secretion in such cases is indicative of duodenal ulcer. However, hypersecretion of acid does not always occur in duodenal ulcer.
  6. To decide the type of surgery to be performed in a patient with peptic ulcer: Raised basal as well as peak acid outputs indicate increased parietal cell mass and need for gastrectomy. Raised basal acid output with normal peak output is an indication for vagotomy.
To assess gastric acid secretion, acid output from the stomach is measured in a fasting state and after injection of a drug which stimulates gastric acid secretion.
 
Basal acid output (BAO) is the amount of hydrochloric acid (HCl) secreted in the absence of any external stimuli (visual, olfactory, or auditory).
 
Maximum acid output (MAO) is the amount of hydrochloric acid secreted by the stomach following stimulation by pentagastrin. MAO is calculated from the first four 15-minute samples after stimulation.
 
Peak acid output (PAO) is calculated from the two highest consecutive 15-minute samples. It indicates greatest possible acid secretory capacity and is preferred over MAO as it is more reproducible.
 
Acidity is estimated by titration.
 
Collection of Sample
 
All drugs that affect gastric acid secretion (e.g. antacids, anticholinergics, cholinergics, H2-receptor antagonists, antihistamines, tranquilizers, antidepressants, and carbonic anhydrase inhibitors) should be withheld for 24 hours before the test. Proton pump inhibitors should be discontinued 5 days prior to the test. Patient should be relaxed and free from all sources of sensory stimulation.
 
Patient should drink or eat nothing after midnight.
 
Gastric juice can be aspirated through an oral or nasogastric tube (polyvinyl chloride, silicone, or polyurethane) or during endoscopy.
 
Oral or nasogastric tube (Figure 855.1) is commonly used. It is a flexible tube having a small diameter and a bulbous end that is made heavy by a small weight of lead. The end is perforated with small holes to allow entry of gastric juice into the tube. As the end is radiopaque, the tube can be positioned in the most dependent part of the stomach under fluoroscopic or X-ray guidance. The tube is lubricated and can be introduced either through the mouth or the nose. The patient is either sitting or reclining on left side. The tube has three or four markings on its outer surface that correspond with distance of the tip of the tube from the teeth, i.e. 40 cm (tip to cardioesophageal junction), 50 cm (body of stomach), 57 cm (pyloric antrum), and 65 cm (duodenum). The position of the tube can be verified either by fluoroscope or by ‘water recovery test’. In the latter test, 50 ml of water is introduced through the tube and aspirated again; recovery of > 90% of water is indicative of proper placement. The tube is usually positioned in the antrum. A syringe is attached to the outer end of the tube for the aspiration of gastric juice.
 
Figure 855.1 Oral or nasogastric Ryles tube
Figure 855.1 Oral or nasogastric Ryle’s tube. The tube is marked at 40, 50, 57, and 65 cm with radiopaque lines for accurate placement. The tip is bulbous and contains a small weight of lead to assist the passage during intubation and to know the position under fluoroscopy or X-ray guidance. There are four perforations or eyes to aspirate contents from the stomach through a syringe attached to the base
 
For estimation of BAO, sample is collected in the morning after 12-hour overnight fast. Gastric secretion that has accumulated overnight is aspirated and discarded. This is followed by aspiration of gastric secretions at 15-minute intervals for 1 hour (i.e. total 4 consecutive samples are collected). All the samples are centrifuged to remove any particulate matter. Each 15-minute sample is analyzed for volume, pH, and acidity. The acid output in the four samples is totaled and the result is expressed as concentration of acid in milliequivalents per hour or in mmol per hour.
 
After the collection of gastric juice for determination of BAO, patient is given a subcutaneous or intramuscular injection of pentagastrin (6 μg/kg of body weight), and immediately afterwards, gastric secretions are aspirated at 15-minute intervals for 1 hour (for estimation of MAO or PAO). MAO is calculated from the first four 15-minute samples after stimulation. PAO is calculated from two consecutive 15-minute samples showing highest acidity.
 
Titration
 
Box 855.1 Determination of basal acid output, maximum acid output, and peak acid output
 
  • Basal acid output (BAO)= Total acid content in all four 15-minute basal samples in mEq/L
  • Maximum acid output (MAO) = Total acid content in all four 15-minute post-pentagastrin samples in mEq/L
  • Peak acid output (PAO) = Sum of two consecutive 15-minute post-pentagastrin samples showing highest acidity ×2 (mEq/L)
Gastric acidity is estimated by titration, with the end point being determined either by noting the change in color of the indicator solution or till the desired pH is reached.
 
In titration, a solution of alkali (0.1 N sodium hydroxide) is added from a graduated vessel (burette) to a known volume of acid (i.e. gastric juice) till the end point or equivalence point of reaction is reached. The concentration of acid is then determined from the concentration and volume of alkali required to neutralize the particular volume of gastric juice. Concentration of acid is expressed in terms of milliequivalents per liter or mmol per liter.
 
Free acidity refers to the concentration of HCl present in a free, uncombined form in a solution. The volume of alkali added to the gastric juice till the Topfer’s reagent (an indicator added earlier to the gastric juice) changes color or when the pH (as measured by the pH meter) reaches 3.5 is a measure of free acidity. A screening test can be carried out for the presence of free HCl in the gastric juice. If red color develops after addition of a drop of Topfer’s reagent to an aliquot of gastric juice, free HCl is present and the diagnosis of pernicious anaemia (achlorhydria) can be excluded.
 
Combined acidity refers to the amount of HCl combined with proteins and mucin and also includes small amount of weak acids present in gastric juice.
 
Total acidity is the sum of free and combined acidity. The amount of alkali added to the gastric juice till phenolphthalein indicator (added earlier to the gastric juice) changes color is a measure of total acidity (Box 855.1).
 
Interpretation of Results
 
  1. Volume: Normal total volume is 20-100 ml (usually < 50 ml). Causes of increased volume of gastric juice are—
    • Delayed emptying of stomach: pyloric stenosis
    • Increased gastric secretion: duodenal ulcer, Zollinger-Ellison syndrome.
  2. Color: Normal gastric secretion is colorless, with a faintly pungent odor. Fresh blood (due to trauma, or recent bleeding from ulcer or cancer) is red in color. Old hemorrhage produces a brown, coffee-ground like appearance (due to formation of acid hematin). Bile regurgitation produces a yellow or green color.
  3. pH: Normal pH is 1.5 to 3.5. In pernicious anemia, pH is greater than 7.0 due to absence of HCl.
  4. Basal acid output:
    • Normal: Up to 5 mEq/hour.
    • Duodenal ulcer: 5-15 mEq/hour.
    • Zollinger-Ellison syndrome: >20 mEq/hour.
    Normal BAO is seen in gastric ulcer and in some patients with duodenal ulcer.
  5. Peak acid output:
    • Normal: 1-20 mEq/hour.
    • Duodenal ulcer: 20-60 mEq/hour.
    • Zollinger-Ellison syndrome: > 60 mEq/hour.
    • Achlorhydria: 0 mEq/hour.
    Normal PAO is seen in gastric ulcer and gastric carcinoma. Values up to 60 mEq/hour can occur in some normal individuals and in some patients with Zollinger-Ellison syndrome.
    In pernicious anemia, there is no acid output due to gastric mucosal atrophy. Achlorhydria should be diagnosed only if there is no free HCl even after maximum stimulation.
  6. Ratio of basal acid output to peak acid output (BAO/PAO):
    • Normal: < 0.20 (or < 20%).
    • Gastric or duodenal ulcer: 0.20-0.40 (20-40%).
    • Duodenal ulcer: 0.40-0.60 (40-60%).
    • Zollinger-Ellison syndrome: > 0.60 (> 60%).
    Normal values occur in gastric ulcer or gastric carcinoma.
 
Conditions associated with change in gastric acid output are listed in Table 855.1.
 
It is to be noted that values of acid output are not diagnostic by themselves and should be correlated with clinical, radiological, and endoscopic features.
 
Table 855.1 Causes of alterations in gastric acid output
Increased gastric acid output Decreased gastric acid output
• Duodenal ulcer Chronic atrophic gastritis
• Zollinger-Ellison syndrome     1. Pernicious anemia
Hyperplasia of antral G cells     2. Rheumatoid arthritis
Systemic mastocytosis     3. Thyrotoxicosis
• Basophilic leukemia • Gastric ulcer
  • Gastric carcinoma
  • Chronic renal failure
  • Post-vagotomy
  • Post-antrectomy

Bioethics

  • 04 Sep 2017
Bioethics is the study of the ethical issues emerging from advances in biology and medicine. It is also moral discernment as it relates to medical policy and practice. Bioethicists are concerned with the ethical questions that arise in the relationships among life sciences, biotechnology, medicine, politics, law, and philosophy. It includes the study of values ("the ethics of the ordinary") relating to primary care and other branches of medicine.
Animal biotechnology is a branch of biotechnology in which molecular biology techniques are used to genetically engineer (i.e. modify the genome of) animals in order to improve their suitability for pharmaceutical, agricultural or industrial applications. Animal biotechnology has been used to produce genetically modified animals that synthesize therapeutic proteins, have improved growth rates or are resistant to disease.

Biophysics

  • 04 Sep 2017
Biophysics or biological physics is an interdisciplinary science that applies the approaches and methods of physics to study biological systems. Biophysics covers all scales of biological organization, from molecular to organismic and populations. Biophysical research shares significant overlap with biochemistry, physical chemistry, nanotechnology, bioengineering, computational biology, biomechanics and systems biology.
 
The term biophysics was originally introduced by Karl Pearson in 1892.

Histopathology

  • 04 Sep 2017
Histopathology (compound of three Greek words: ἱστός histos "tissue", πάθος pathos "suffering", and -λογία -logia"study of") refers to the microscopic examination of tissue in order to study the manifestations of disease. Specifically, in clinical medicine, histopathology refers to the examination of a biopsy or surgical specimen by a pathologist, after the specimen has been processed and histological sections have been placed onto glass slides. In contrast, cytopathology examines (1) free cells or (2) tissue micro-fragments (as "cell blocks").

Physiology

  • 04 Sep 2017
Physiology (/ˌfɪziˈɒləi/; from Ancient Greek φύσις (physis), meaning 'nature, origin', and -λογία (-logia), meaning 'study of') is the scientific study of normal mechanisms, and their interactions, which works within a living system. A sub-discipline of biology, its focus is in how organisms, organ systems, organs, cells, and biomolecules carry out the chemical or physical functions that exist in a living system. Given the size of the field, it is divided into, among others, animal physiology (including that of humans), plant physiology, cellular physiology, microbial physiology (microbial metabolism), bacterial physiology, and viral physiology.
 
Central to an understanding of physiological functioning is its integrated nature with other disciplines such as chemistry and physics, coordinated homeostatic control mechanisms, and continuous communication between cells.
 
The Nobel Prize in Physiology or Medicine is awarded to those who make significant achievements in this discipline by the Royal Swedish Academy of Sciences. In medicine, a physiologic state is one occurring from normal body function, rather than pathologically, which is centered on the abnormalities that occur in animal diseases, including humans.

Food Science

  • 04 Sep 2017
Food science is the applied science devoted to the study of food. The Institute of Food Technologists defines food science as "the discipline in which the engineering, biological, and physical sciences are used to study the nature of foods, the causes of deterioration, the principles underlying food processing, and the improvement of foods for the consuming public". The textbook Food Science defines food science in simpler terms as "the application of basic sciences and engineering to study the physical, chemical, and biochemical nature of foods and the principles of food processing".

Ecology

  • 04 Sep 2017
Ecology (from Greek: οἶκος, "house", or "environment"; -λογία, "study of") is the scientific analysis and study of interactions among organisms and their environment. It is an interdisciplinary field that includes biology, geography, and Earth science. Ecology includes the study of interactions that organisms have with each other, other organisms, and with abiotic components of their environment. Topics of interest to ecologists include the diversity, distribution, amount (biomass), and number (population) of particular organisms, as well as cooperation and competition between organisms, both within and among ecosystems. Ecosystems are composed of dynamically interacting parts including organisms, the communities they make up, and the non-living components of their environment. Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and various niche construction activities, regulate the flux of energy and matter through an environment. These processes are sustained by organisms with specific life history traits, and the variety of organisms is called biodiversity. Biodiversity, which refers to the varieties of species, genes, and ecosystems, enhances certain ecosystem services.
 
Ecology is not synonymous with environment, environmentalism, natural history, or environmental science. It is closely related to evolutionary biology, genetics, and ethology. An important focus for ecologists is to improve the understanding of how biodiversity affects ecological function. Ecologists seek to explain:
 
  • Life processes, interactions, and adaptations
  • The movement of materials and energy through living communities
  • The successional development of ecosystems
  • The abundance and distribution of organisms and biodiversity in the context of the environment.
 
There are many practical applications of ecology in conservation biology, wetland management, natural resource management(agroecology, agriculture, forestry, agroforestry, fisheries), city planning (urban ecology), community health, economics, basic and applied science, and human social interaction (human ecology). For example, the Circles of Sustainability approach treats ecology as more than the environment 'out there'. It is not treated as separate from humans. Organisms (including humans) and resources compose ecosystems which, in turn, maintain biophysical feedback mechanisms that moderate processes acting on living (biotic) and non-living (abiotic) components of the planet. Ecosystems sustain life-supporting functions and produce natural capital like biomass production (food, fuel, fiber, and medicine), the regulation of climate, global biogeochemical cycles, water filtration, soil formation, erosion control, flood protection, and many other natural features of scientific, historical, economic, or intrinsic value.
 
The word "ecology" ("Ökologie") was coined in 1866 by the German scientist Ernst Haeckel (1834–1919). Ecological thought is derivative of established currents in philosophy, particularly from ethics and politics. Ancient Greek philosophers such as Hippocrates and Aristotle laid the foundations of ecology in their studies on natural history. Modern ecology became a much more rigorous science in the late 19th century. Evolutionary concepts relating to adaptation and natural selection became the cornerstones of modern ecological theory.

Forensic Science

  • 04 Sep 2017
Forensic science is the application of science to criminal and civil laws, mainly—on the criminal side—during criminal investigation, as governed by the legal standards of admissible evidence and criminal procedure.
 
Forensic scientists collect, preserve, and analyze scientific evidence during the course of an investigation. While some forensic scientists travel to the scene of the crime to collect the evidence themselves, others occupy a laboratory role, performing analysis on objects brought to them by other individuals.
 
In addition to their laboratory role, forensic scientists testify as expert witnesses in both criminal and civil cases and can work for either the prosecution or the defense. While any field could technically be forensic, certain sections have developed over time to encompass the majority of forensically related cases.

Microscopic examinations done on fecal sample are shown in Figure 846.1.

Collection of Specimen for Parasites

A random specimen of stool (at least 4 ml or 4 cm³) is collected in a clean, dry, container with a tightly fitting lid (a tin box, plastic box, glass jar, or waxed cardboard box) and transported immediately to the laboratory (this is because trophozoites of Entameba histolytica rapidly degenerate and alter in morphology). About 20-40 grams of formed stool or 5-6 tablespoons of watery stool should be collected. Stool should not be contaminated with urine, water, soil, or menstrual blood. Urine and water destroy trophozoites; soil will introduce extraneous organisms and also hinder proper examination. Parasites are best detected in warm, freshly passed stools and therefore stools should be examined as early as possible after receipt in the laboratory (preferably within 1 hour of collection). If delay in examination is anticipated, sample may be refrigerated. A fixative containing 10% formalin (for preservation of eggs, larvae, and cysts) or polyvinyl alcohol (for preservation of trophozoites and cysts, and for permanent staining) may be used if specimen is to be transported to a distant laboratory.

Figure 846.1 Microscopic examinations carried out on fecal sample
Figure 846.1 Microscopic examinations carried out on fecal sample

One negative report for ova and parasites does not exclude the possibility of infection. Three separate samples, collected at 3-day intervals, have been recommended to detect all parasite infections.

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Patient should not be receiving oily laxatives, antidiarrheal medications, bismuth, antibiotics like tetracycline, or antacids for 7 days before stool examination. Patient should not have undergone a barium swallow examination.

In the laboratory, macroscopic examination is done for consistency (watery, loose, soft or formed) (Figure 846.2), color, odor, and presence of blood, mucus, adult worms or segments of tapeworms.

Figure 846.2 Consistency of feces
Figure 846.2 Consistency of feces

Trophozoites are most likely to be found in loose or watery stools or in stools containing blood and mucus, while cysts are likely to be found in formed stools. Trophozoites die soon after being passed and therefore such stools should be examined within 1 hour of passing. Examination of formed stools can be delayed but should be completed on the same day.

Color/Appearance of Fecal Specimens

  • Brown: Normal
  • Black: Bleeding in upper gastrointestinal tract (proximal to cecum), Drugs (iron salts, bismuth salts, charcoal)
  • Red: Bleeeding in large intestine, undigested tomatoes or beets
  • Clay-colored (gray-white): Biliary obstruction
  • Silvery: Carcinoma of ampulla of Vater
  • Watery: Certain strains of Escherichia coli, Rotavirus enteritis, cryptosporidiosis
  • Rice water: Cholera
  • Unformed with blood and mucus: Amebiasis, inflammatory bowel disease
  • Unformed with blood, mucus, and pus: Bacillary dysentery
  • Unformed, frothy, foul smelling, which float on water: Steatorrhea.

Preparation of Slides

After receipt in the laboratory, saline and iodine wet mounts of the sample are prepared (Figure 846.3).

Figure 846.3 Saline and iodine wet mounts of fecal sample
Figure 846.3 Saline and iodine wet mounts of fecal sample

A drop of normal saline is placed near one end of a glass slide and a drop of Lugol iodine solution is placed near the other end. A small amount of feces (about the size of a match-head) is mixed with a drop each of saline and iodine using a wire loop, and a cover slip is placed over each preparation separately. If the specimen contains blood or mucus, that portion should be included for examination (trophozoites are more readily found in mucus). If the stools are liquid, select the portion from the surface for examination.

Saline wet mount is used for demonstration of eggs and larvae of helminths, and trophozoites and cysts of protozoa. It can also detect red cells and white cells. Iodine stains glycogen and nuclei of the cysts. The iodine wet mount is useful for identification of protozoal cysts. Trophozoites become non-motile in iodine mounts. A liquid, diarrheal stool can be examined directly without adding saline.

Concentration Procedure

Concentration of fecal specimen is useful if very small numbers of parasites are present. However, in concentrated specimens, amebic trophozoites can no longer be detected since they are destroyed. If wet mount examination is negative and there is clinical suspicion of parasitic infection, fecal concentration is indicated. It is used for detection of ova, cysts, and larvae of parasites.

Various concentration methods are available; the choice depends on the nature of parasites to be identified and the equipment/reagent available in a particular laboratory. Concentration techniques are of two main types:

  • Sedimentation techniques: Ova and cysts settle at the bottom. However, excessive fecal debris may make the detection of parasites difficult. Example: Formolethyl acetate sedimentation procedure.
  • Floatation techniques: Ova and cysts float on surface. However, some ova and cysts do not float at the top in this procedure. Examples: Saturated salt floatation technique and zinc sulphate concentration technique.

The most commonly used sedimentation method is formol-ethyl acetate concentration method since: (i) it can detect eggs and larvae of almost all helminths, and cysts of protozoa, (ii) it preserves their morphology well, (iii) it is rapid, and (iv) risk of infection to the laboratory worker is minimal because pathogens are killed by formalin.

In this method, fecal suspension is prepared in 10% formalin (10 ml formalin + 1 gram feces). This suspension is then passed through a gauze filter till 7 ml of filtered material is obtained. To this, ethyl acetate (3 ml) is added and the mixture is centrifuged for 1 minute. Eggs, larvae, and cysts sediment at the bottom of the centrifuge tube (Figure 846.4). Above this deposit, there are layers of formalin, fecal debris, and ether. Fecal debris is loosened with an applicator stick and the supernatant is poured off. One drop of sediment is placed on one end of a glass slide and one drop is placed at the other end. One of the drops is stained with iodine, cover slips are placed, and the preparation is examined under the microscope.

Figure 846.4 Formol ethyl acetate concentration technique
Figure 846.4 Formol-ethyl acetate concentration technique

Classification of Intestinal Parasites of Humans

Intestinal parasites of humans are classified into two main kingdoms: protozoa and metazoa (helminths) (Figure 846.5).

Figure 846.5 Classification of intestinal parasites of humans
Figure 846.5 Classification of intestinal parasites of humans

Chemical examination of feces is usually carried out for the following tests (Figure 845.1):

  • Occult blood
  • Excess fat excretion (malabsorption)
  • Urobilinogen
  • Reducing sugars
  • Fecal osmotic gap
  • Fecal pH
Figure 845.17 Chemical examinations done on fecal sample
Figure 845.1 Chemical examinations done on fecal sample

Test for Occult Blood in Stools

Presence of blood in feces which is not apparent on gross inspection and which can be detected only by chemical tests is called as occult blood. Causes of occult blood in stools are:

  1. Intestinal diseases: hookworms, amebiasis, typhoid fever, ulcerative colitis, intussusception, adenoma, cancer of colon or rectum.
  2. Gastric and esophageal diseases: peptic ulcer, gastritis, esophageal varices, hiatus hernia.
  3. Systemic disorders: bleeding diathesis, uremia.
  4. Long distance runners.

Occult blood test is recommended as a screening procedure for detection of asymptomatic colorectal cancer. Yearly examinations should be carried out after the age of 50 years. If the test is positive, endoscopy and barium enema are indicated.

Tests for detection of occult blood in feces: Many tests are available which differ in their specificity and sensitivity. These tests include tests based on peroxidase-like activity of hemoglobin (benzidine, orthotolidine, aminophenazone, guaiac), immunochemical tests, and radioisotope tests.

article continued below

Tests Based on Peroxidase-like Activity of Hemoglobin

Principle: Hemoglobin has peroxidase-like activity and releases oxygen from hydrogen peroxide. Oxygen molecule then oxidizes the chemical reagent (benzidine, orthotolidine, aminophenazone, or guaiac) to produce a colored reaction product.

Benzidine and orthotolidine are carcinogenic and are no longer used. Benzidine test is also highly sensitive and false-positive reactions are common. Since bleeding from the lesion may be intermittent, repeated testing may be required.

Causes of False-positive Tests

  1. Ingestion of peroxidase-containing foods like red meat, fish, poultry, turnips, horseradish, cauliflower, spinach, or cucumber. Diet should be free from peroxidase-containing foods for at least 3 days prior to testing.
  2. Drugs like aspirin and other anti-inflammatory drugs, which increase blood loss from gastrointestinal tract in normal persons.

Causes of False-negative Tests

  1. Foods containing large amounts of vitamin C.
  2. Conversion of all hemoglobin to acid hematin (which has no peroxidase-like activity) during passage through the gastrointestinal tract.

Immunochemical Tests

These tests specifically detect human hemoglobin. Therefore there is no interference from animal hemoglobin or myoglobin (e.g. meat) or peroxidase-containing vegetables in the diet.

The test consists of mixing the sample with latex particles coated with anti-human haemoglobin antibody, and if agglutination occurs, test is positive. This test can detect 0.6 ml of blood per 100 grams of feces.

Radioisotope Test Using 51Cr

In this test, 10 ml of patient’s blood is withdrawn, labeled with 51Cr, and re-infused intravenously. Radioactivity is measured in fecal sample and in simultaneously collected blood specimen. Radioactivity in feces indicates gastrointestinal bleeding. Amount of blood loss can be calculated. Although the test is sensitive, it is not suitable for routine screening.

Apt test: This test is done to decide whether blood in the vomitus or in the feces of a neonate represents swallowed maternal blood or is the result of bleeding in the gastrointestinal tract. The test was devised by Dr. Apt and hence the name. The baby swallows blood during delivery or during breastfeeding if nipples are cracked. Apt test is based on the principle that if blood is of neonatal origin it will contain high proportion of hemoglobin F (Hb F) that is resistant to alkali denaturation. On the other hand, maternal blood mostly contains adult hemoglobin or Hb A that is less resistant.

Test for Malabsorption of Fat

Dietary fat is absorbed in the small intestine with the help of bile salts and pancreatic lipase. Fecal fat mainly consists of neutral fats (unsplit fats), fatty acids, and soaps (fatty acid salts). Normally very little fat is excreted in feces (<7 grams/day in adults). Excess excretion of fecal fat indicates malabsorption and is known as steatorrhea. It manifests as bulky, frothy, and foul-smelling stools, which float on the surface of water.

Causes of Malabsorption of Fat

  1. Deficiency of pancreatic lipase (insufficient lipolysis): chronic pancreatitis, cystic fibrosis.
  2. Deficiency of bile salts (insufficient emulsification of fat): biliary obstruction, severe liver disease, bile salt deconjugation due to bacterial overgrowth in the small intestine.
  3. Diseases of small intestine: tropical sprue, celiac disease, Whipple’s disease.

Tests for fecal fat are qualitative (i.e. direct microscopic examination after fat staining), and quantitative (i.e. estimation of fat by gravimetric or titrimetric analysis).

  1. Microscopic stool examination after staining for fat: A random specimen of stool is collected after putting the patient on a diet of >80 gm fat per day. Stool sample is stained with a fat stain (oil red O, Sudan III, or Sudan IV) and observed under the microscope for fat globules (Figure 845.2). Presence of ≥60 fat droplets/HPF indicates steatorrhea. Ingestion of mineral or castor oil and use of rectal suppositories can cause problems in interpretation.
  2. Quantitative estimation of fecal fat: The definitive test for diagnosis of fat malabsorption is quantitation of fecal fat. Patient should be on a diet of 70-100 gm of fat per day for 6 days before the test. Feces are collected over 72 hours and stored in a refrigerator during the collection period. Specimen should not be contaminated with urine. Fat quantitation can be done by gravimetric or titrimetric method. In gravimetric method, an accurately weighed sample of feces is emulsified, acidified, and fat is extracted in a solvent; after evaporation of solvent, fat is weighed as a pure compound. Titrimetric analysis is the most widely used method. An accurately weighed stool sample is treated with alcoholic potassium hydroxide to convert fat into soaps. Soaps are then converted to fatty acids by the addition of hydrochloric acid. Fatty acids are extracted in a solvent and the solvent is evaporated. The solution of fat made in neutral alcohol is then titrated against sodium hydroxide. Fatty acids comprise about 80% of fecal fat. Values >7 grams/day are usually abnormal. Values >14 grams/day are specific for diseases causing fat malabsorption.
Figure 845.2 Sudan stain on fecal sample
Figure 845.2 Sudan stain on fecal sample: (A) Negative; (B) Positive

Test for Urobilinogen in Feces

Fecal urobilinogen is determined by Ehrlich’s aldehyde test (see  Article “Test for Detection of Urobilinogen in Urine). Specimen should be fresh and kept protected from light. Normal amount of urobilinogen excreted in feces is 50-300 mg per day. Increased fecal excretion of urobilinogen is seen in hemolytic anemia. Urobilinogen is deceased in biliary tract obstruction, severe liver disease, oral antibiotic therapy (disturbance of intestinal bacterial flora), and aplastic anemia (low hemoglobin turnover). Stools become pale or clay-colored if urobilinogen is reduced or absent.

Test for Reducing Sugars

Deficiency of intestinal enzyme lactase is a common cause of malabsorption. Lactase converts lactose (in milk) to glucose and galactose. If lactase is deficient, lactose is converted to lactic acid with production of gas. In infants this leads to diarrhea, vomiting, and failure to thrive. Benedict’s test or Clinitest™ tablet test for reducing sugars is used to test freshly collected stool sample for lactose. In addition, oral lactose tolerance test is abnormal (after oral lactose, blood glucose fails to rise above 20 mg/dl of basal value) in lactase deficiency. Rise in blood glucose indicates that lactose has been hydrolysed and absorbed by the mucosa. Lactose tolerance test is now replaced by lactose breath hydrogen testing. In lactase deficiency, accumulated lactose in the colon is rapidly fermented to organic acids and gases like hydrogen. Hydrogen is absorbed and then excreted through the lungs into the breath. Amount of hydrogen is then measured in breath; breath hydrogen more than 20 ppm above baseline within 4 hours indicates positive test.

Fecal Osmotic Gap

Fecal osmotic gap is calculated from concentration of electrolytes in stool water by formula 290-2([Na+] + [K+]). (290 is the assumed plasma osmolality). In osmotic diarrheas, osmotic gap is >150 mOsm/kg, while in secretory diarrhea, it is typically below 50 mOsm/kg. Evaluation of chronic diarrhea is shown in Figure 845.3.

Figure 845.3 Evaluation of chronic diarrhea
Figure 845.3 Evaluation of chronic diarrhea

Fecal pH

Stool pH below 5.6 is characteristic of carbohydrate malabsorption.

Tests to Assess Proximal Tubular Function
 
Renal tubules efficiently reabsorb 99% of the glomerular filtrate to conserve the essential substances like glucose, amino acids, and water.
 
1. Glycosuria: In renal glycosuria, glucose is excreted in urine, while blood glucose level is normal. This is because of a specific tubular lesion which leads to impairment of glucose reabsorption. Renal glycosuria is a benign condition. Glycosuria can also occur in Fanconi syndrome.
 
2. Generalized aminoaciduria: In proximal renal tubular dysfunction, many amino acids are excreted in urine due to defective tubular reabsorption.
 
3. Tubular proteinuria (Low molecular weight proteinuria): Normally, low molecular weight proteins2 –microglobulin, retinol-binding protein, lysozyme, and α1 –microglobulin) are freely filtered by glomeruli and are completely reabsorbed by proximal renal tubules. With tubular damage, these low molecular weight proteins are excreted in urine and can be detected by urine protein electrophoresis. Increased amounts of these proteins in urine are indicative of renal tubular damage.
 
4. Urinary concentration of sodium: If both BUN and serum creatinine are acutely increased, it is necessary to distinguish between prerenal azotemia (renal underperfusion) and acute tubular necrosis. In prerenal azotemia, renal tubules are functioning normally and reabsorb sodium, while in acute tubular necrosis, tubular function is impaired and sodium absorption is decreased. Therefore, in prerenal azotemia, urinay sodium concentration is < 20 mEq/L while in acute tubular necrosis, it is > 20 mEq/L.
 
5. Fractional excretion of sodium (FENa): Measurement of urinary sodium concentration is affected by urine volume and can produce misleading results. Therefore, to avoid this, fractional excretion of sodium is calculated. This refers to the percentage of filtered sodium that has been absorbed and percentage that has been excreted. Measurement of fractional sodium excretion is a better indicator of tubular absorption of sodium than quantitation of urine sodium alone.
 
This test is indicated in acute renal failure. In oliguric patients, this is the most reliable means of early distinction between pre-renal failure and renal failure due to acute tubular necrosis. It is calculated from the following formula:
 
 
(Urine sodium × Plasma creatinine) × 100%
(Plasma sodium × Urine creatinine)
 
 
In pre-renal failure this ratio is less than 1%, and in acute tubular necrosis it is more than 1%. In pre-renal failure (due to reduced renal perfusion), aldosterone secretion is stimulated which causes maximal sodium conservation by the tubules and the ratio is less than 1%. In acute tubular necrosis, maximum sodium reabsorption is not possible due to tubular cell injury and consequently the ratio will be more than 1%. Values above 3% are strongly suggestive of acute tubular necrosis.
 
Tests to Assess Distal Tubular Function
 
1. Urine specific gravity: Normal specific gravity is 1.003 to 1.030. It depends on state of hydration and fluid intake.
 
  1. Causes of increased specific gravity:
    a. Reduced renal perfusion (with preservation of concentrating ability of tubules),
    b. Proteinuria,
    c. Glycosuria,
    d. Glomerulonephritis.
    e. Urinary tract obstruction.
  2. Causes of reduced specific gravity:
    a. Diabetes insipidus
    b. Chronic renal failure
    c. Impaired concentrating ability due to diseases of tubules.
 
As a test of renal function, it gives information about the ability of renal tubules to concentrate the glomerular filtrate. This concentrating ability is lost in diseases of renal tubules.
 
Fixed specific gravity of 1.010, which cannot be lowered or increased by increasing or decreasing the fluid intake respectively, is an indication of chronic renal failure.
 
2. Urine osmolality: The most commonly employed test to evaluate tubular function is measurement of urine/plasma osmolality. This is the most sensitive method for determination of ability of concentration. Osmolality measures number of dissolved particles in a solution. Specific gravity, on the other hand, is the ratio of mass of a solution to the mass of water i.e. it measures total mass of solute. Specific gravity depends on both the number and the nature of dissolved particles while osmolality is exact number of solute particles in a solution. Specific gravity measurement can be affected by the presence of solutes of large molecular weight like proteins and glucose, while osmolality is not. Therefore measurement of osmolality is preferred.
 
When solutes are dissolved in a solvent, certain changes take place like lowering of freezing point, increase in boiling point, decrease in vapor pressure, or increase of osmotic pressure of the solvent. These properties are made use of in measuring osmolality by an instrument called as osmometer.
 
Osmolality is expressed as milliOsmol/kg of water.
 
Urine/plasma osmolality ratio is helpful in distinguishing pre-renal azotemia (in which ratio is higher) from acute renal failure due to acute tubular necrosis (in which ratio is lower). If urine and plasma osmolality are almost similar, then there is defective tubular reabsorption of water.
 
3. Water deprivation test: If the value of baseline osmolality of urine is inconclusive, then water deprivation test is performed. In this test, water intake is restricted for a specified period of time followed by measurement of specific gravity or osmolality. Normally, urine osmolality should rise in response to water deprivation. If it fails to rise, then desmopressin is administered to differentiate between central diabetes insipidus and nephrogenic diabetes insipidus. Urinary concentration ability is corrected after administration of desmopressin in central diabetes insipidus, but not in nephrogenic diabetes insipidus.
 
If urine osmolality is > 800 mOsm/kg of water or specific gravity is ≥1.025 following dehydration, concentrating ability of renal tubules is normal. However, normal result does not rule out presence of renal disease.
False result will be obtained if the patient is on low-salt, low-protein diet or is suffering from major electrolyte and water disturbance.
 
4. Water loading antidiuretic hormone suppression test: This test assesses the capacity of the kidney to make urine dilute after water loading.
 
After overnight fast, patient empties the bladder and drinks 20 ml/kg of water in 15-30 minutes. The urine is collected at hourly intervals for the next 4 hours for measurements of urine volume, specific gravity, and osmolality. Plasma levels of antidiuretic hormone and serum osmolality should be measured at hourly intervals.
 
Normally, more than 90% of water should be excreted in 4 hours. The specific gravity should fall to 1.003 and osmolality should fall to < 100 mOsm/kg. Plasma level of antidiuretic hormone should be appropriate for serum osmolality. In renal function impairment, urine volume is reduced (<80% of fluid intake is excreted) and specific gravity and osmolality fail to decrease. The test is also impaired in adrenocortical insufficiency, malabsorption, obesity, ascites, congestive heart failure, cirrhosis, and dehydration.
 
This test is not advisable in patients with cardiac failure or kidney disease. If there is failure to excrete water load, fatal hyponatremia can occur.
 
5. Ammonium chloride loading test (Acid load test): Diagnosis of renal tubular acidosis is usually considered after excluding other causes of metabolic acidosis. This test is considered as a ‘gold standard’ for the diagnosis of distal or type 1 renal tubular acidosis. Urine pH and plasma bicarbonate are measured after overnight fasting. If pH is less than 5.4, acidifying ability of renal tubules is normal. If pH is greater than 5.4 and plasma bicarbonate is low, diagnosis of renal tubular acidosis is confirmed. In both the above cases, further testing need not be performed. In all other cases in which neither of above results is obtained, further testing is carried out. Patient is given ammonium chloride orally (0.1 gm/kg) over 1 hour after overnight fast and urine samples are collected hourly for next 6-8 hours. Ammonium ion dissociates into H+ and NH3. Ammonium chloride makes blood acidic. If pH is less than 5.4 in any one of the samples, acidifying ability of the distal tubules is normal.
Normally, a very small amount of albumin is excreted in urine. The earliest evidence of glomerular damage in diabetes mellitus is occurrence of microalbuminuria (albuminuria in the range of 30 to 300 mg/24 hours). An albuminuria > 300-mg/24 hour is termed clinical or overt and indicates significant glomerular damage. (See “Proteinuria” under Article “Chemical Examination of Urine”).
Two biochemical parameters are commonly used to assess renal function: blood urea nitrogen (BUN) and serum creatinine. Although convenient, they are insensitive markers of glomerular function.
 
Blood Urea Nitrogen (BUN)
 
Urea is produced in the liver from amino acids (ingested or tissue-derived). Amino acids are utilized to produce energy, synthesize proteins, and are catabolized to ammonia. Urea is produced in the liver from ammonia in the Krebs urea cycle. Ammonia is toxic and hence is converted to urea, which is then excreted in urine (Figure 842.1).
 
Figure 842.1 Formation of urea from protein breakdown
Figure 842.1 Formation of urea from protein breakdown 
 
The concentration of blood urea is usually expressed as blood urea nitrogen. This is because older methods estimated only the nitrogen in urea. Molecular weight of urea is 60, and 28 grams of nitrogen are present in a gm mole of urea. As the relationship between urea and BUN is 60/28, BUN can be converted to urea by multiplying BUN by 2.14, i.e. the real concentration of urea is BUN × (60/28).
 
Urea is completely filtered by the glomeruli, and about 30-40% of the filtered amount is reabsorbed in the renal tubules depending on the person’s state of hydration.
 
Blood level of urea is affected by a number of non-renal factors (e.g. high protein diet, upper gastrointestinal hemorrhage, liver function, etc.) and therefore utility of BUN as an indicator of renal function is limited. Also considerable destruction of renal parenchyma is required before elevation of blood urea can occur.
 
The term azotemia refers to the increase in the blood level of urea; uremia is the clinical syndrome resulting from this increase. If renal function is absent, BUN rises by 10-20 mg/dl/day.
 
Causes of increased BUN:
 
  1. Pre-renal azotemia: shock, congestive heart failure, salt and water depletion
  2. Renal azotemia: impairment of renal function
  3. Post-renal azotemia: obstruction of urinary tract
  4. Increased rate of production of urea:
    • High protein diet
    • Increased protein catabolism (trauma, burns, fever)
    • Absorption of amino acids and peptides from a large gastrointestinal hemorrhage or tissue hematoma
 
Methods for estimation of BUN:
 
Two methods are commonly used.
 
  1. Diacetyl monoxime urea method: This is a direct method. Urea reacts with diacetyl monoxime at high temperature in the presence of a strong acid and an oxidizing agent. Reaction of urea and diacetyl monoxime produces a yellow diazine derivative. The intensity of color is measured in a colorimeter or spectrophotometer.
  2. Urease- Berthelot reaction: This is an indirect method. Enzyme urease splits off ammonia from the urea molecule at 37°C. Ammonia generated is then reacted with alkaline hypochlorite and phenol with a catalyst to produce a stable color (indophenol). Intensity of color produced is then measured in a spectrophotometer at 570 nm.
 
Reference range for BUN in adults is 7-18 mg/dl. In adults > 60 years, level is 8-21 mg/dl.
 
Serum Creatinine
 
Creatinine is a nitrogenous waste product formed in muscle from creatine phosphate. Endogenous production of creatinine is proportional to muscle mass and body weight. Exogenous creatinine (from ingestion of meat) has little effect on daily creatinine excretion.
 
Serum creatinine is a more specific and more sensitive indicator of renal function as compared to BUN because:
 
  • It is produced from muscles at a constant rate and its level in blood is not affected by diet, protein catabolism, or other exogenous factors;
  • It is not reabsorbed, and very little is secreted by tubules.
 
With muscle mass remaining constant, increased creatinine level reflects reduction of glomerular filtration rate. However, because of significant kidney reserve, increase of serum creatinine level (from 1.0 mg/dl to 2.0 mg/dl) in blood does not occur until about 50% of kidney function is lost. Therefore, serum creatinine is not a sensitive indicator of early renal impairment. Also, laboratory report showing serum creatinine “within normal range” does not necessarily mean that the level is normal; the level should be correlated with body weight, age, and sex of the individual. If renal function is absent, serum creatinine rises by 1.0 to 1.5 mg/dl/day (Figure 842.2).
 
Figure 842.2 Relationship between glomerular filtration rate and serum creatinine
Figure 842.2 Relationship between glomerular filtration rate and serum creatinine. Significant increase of serum creatinine does not occur till a considerable fall in GFR

Causes of Increased Serum Creatinine Level
 
  1. Pre-renal, renal, and post-renal azotemia
  2. Large amount of dietary meat
  3. Active acromegaly and gigantism
 
Causes of Decreased Serum Creatinine Level
 
  1. Pregnancy
  2. Increasing age (reduction in muscle mass)
 
Methods for Estimation of Serum Creatinine
 
The test for serum creatinine is cheap, readily available, and simple to perform. There are two methods that are commonly used:
 
  1. Jaffe’s reaction (Alkaline picrate reaction): This is the most widely used method. Creatinine reacts with picrate in an alkaline solution to produce spectrophotometer at 485 nm. Certain substances in plasma (such as glucose, protein, fructose, ascorbic acid, acetoacetate, acetone, and cephalosporins) react with picrate in a similar manner; these are called as non-creatinine chromogens (and can cause false elevation of serum creatinine level). Thus ‘true’ creatinine is less by 0.2 to 0.4 mg/dl when estimated by Jaffe’s reaction.
  2. Enzymatic methods: These methods use enzymes that cleave creatinine; hydrogen peroxide produced then reacts with phenol and a dye to produce a colored product, which is measured in a spectrophotometer.
 
Reference range:
 
Adult males: 0.7-1.3 mg/dl.
Adult females: 0.6-1.1 mg/dl.
 
Serum creatinine alone should not be used to assess renal function. This is because serum creatinine concentration depends on age, sex, muscle mass, glomerular filtration and amount of tubular secretion. Thus, normal serum creatinine range is wide. Serum creatinine begins to rise when GFR falls below 50% of normal. Minor rise of serum creatinine is associated with significant reduction of GFR (Figure 842.2). Therefore early stage of chronic renal impairment cannot be detected by measurement of serum creatinine alone.
 
BUN/Serum Creatinine Ratio
 
Clinicians commonly calculate BUN/creatinine ratio to discriminate pre-renal and post-renal azotemia from renal azotemia. Normal ratio is 12:1 to 20:1.
 
Causes of Increased BUN/Creatinine Ratio (>20:1):
 
  1. Increased BUN with normal serum creatinine:
    • Pre-renal azotemia (reduced renal perfusion)
    • High protein diet
    • Increased protein catabolism
    • Gastrointestinal hemorrhage
  2. Increase of both BUN and serum creatinine with disproportionately greater increase of BUN:
    • Post-renal azotemia (Obstruction to the outflow of urine)
    Obstruction to the urine outflow causes diffusion of urinary urea back into the blood from tubules because of backpressure.

Causes of Decreased BUN/Creatinine Ratio (<10:1)
 
  • Acute tubular necrosis
  • Low protein diet, starvation
  • Severe liver disease
One can estimate GFR from age, sex, body weight, and serum creatinine value of a person from the following formula (Cockcroft and Gault):
 
 
Creatinine clearance in ml/min = (140 - Age in years) × (Body weight in kg)
                                                              (72 × Serum creatinine in mg/dl)
 
 
In females, the value obtained from above equation is multiplied by 0.85 to get the result.
 
It is recommended by National Kidney Foundation (USA) to calculate creatinine clearance by Cockcroft and Gault or other equation from serum creatinine value rather than estimating creatinine clearance from a 24-hour urine sample. This is because the latter test is inconvenient, time-consuming, and often inaccurate.
Glomerular filtration rate refers to the rate in ml/min at which a substance is cleared from the circulation by the glomeruli. The ability of the glomeruli to filter a substance from the blood is assessed by clearance studies. If a substance is not bound to protein in plasma, is completely filtered by the glomeruli, and is neither secreted nor reabsorbed by the tubules, then its clearance rate is equal to the glomerular filtration rate (GFR). Clearance of a substance refers to the volume of plasma, which is completely cleared of that substance per minute; it is calculated from the following formula:
 
Clearance = UV
                      P
 
where, U = concentration of a substance in urine in mg/dl; V = volume of urine excreted in ml/min; and P = concentration of the substance in plasma in mg/dl. Since U and P are in the same units, they cancel each other and the clearance value is expressed in the same unit as V i.e. ml/min. All clearance values are adjusted to a standard body surface area i.e. 1.73 m2.

The agents used for measurement of GFR are:
 
  • Exogenous: Inulin, Radiolabelled ethylenediamine tetraacetic acid (51Cr- EDTA), 125I-iothalamate
  • Endogenous: Creatinine, Urea, Cystatin C
 
The agent used for measurement of GFR should have following properties: (1) It should be physiologically inert and preferably endogenous, (2) It should be freely filtered by glomeruli and should be neither reabsorbed nor secreted by renal tubules, (3) It should not bind to plasma proteins and should not be metabolized by kidneys, and (4) It should be excreted only by the kidneys. However, there is no such ideal endogenous agent.
 
Clearance tests are cumbersome to perform, expensive, and not readily available. One major problem with clearance studies is incomplete urine collection.
 
Abnormal clearance occurs in: (i) pre-renal factors: reduced blood flow due to shock, dehydration, and congestive cardiac failure; (ii) renal diseases; and (iii) obstruction to urinary outflow.
 
Inulin Clearance
 
Inulin, an inert plant polysaccharide (a fructose polymer), is filtered by the glomeruli and is neither reabsorbed nor secreted by the tubules; therefore it is an ideal agent for measuring GFR. A bolus dose of inulin (25 ml of 10% solution IV) is administered followed by constant intravenous infusion (500 ml of 1.5% solution at the rate of 4 ml/min). Timed urine samples are collected and blood samples are obtained at the midpoint of timed urine collection. This test is considered as the ‘gold standard’ (or reference method) for estimation of GFR. However, this test is rarely used because it is time consuming, expensive, constant intravenous infusion of inulin is needed to maintain steady plasma level, and difficulties in laboratory analysis. Average inulin clearance for males is 125 ml/min/1.73 m2 and for females is 110 ml/min/1.73 m2. In children less than 2 years and in older adults, clearance is low. This test is largely limited to clinical research.
 
Clearance of Radiolabeled Agents
 
Urinary clearance of radiolabeled iothalamate (125Iiothalamate) correlates closely with inulin clearance. However, this method is expensive with risk of exposure to radioactive substances. Other radiolabelled substances used are 51Cr-EDTA and 99Tc-DTPA.
 
Cystatin C Clearance
 
This is a cysteine protease inhibitor of MW 13,000, which is produced at a constant rate by all the nucleated cells. It is not bound to protein, is freely filtered by glomeruli and is not returned to circulation after filtration. It is a more sensitive and specific marker of impaired renal function than plasma creatinine. Its level is not affected by sex, diet, or muscle mass. It is thought that cystatin C is a superior marker for estimation of GFR than creatinine clearance. It is measured by immunoassay.
 
Creatinine Clearance
 
This is the most commonly used test for measuring GFR.
 
Creatinine is being produced constantly from creatine in muscle. It is completely filtered by glomeruli and is not reabsorbed by tubules; however, a small amount is secreted by tubules.
 
A 24-hour urine sample is preferred to overcome the problem of diurnal variation of creatinine excretion and to reduce the inaccuracy in urine collection. 
 
After getting up in the morning, the first voided urine is discarded. Subsequently all the urine passed is collected in the container provided. After getting up in the next morning, the first voided urine is also collected and the container is sent to the laboratory. A blood sample for estimation of plasma creatinine is obtained at midpoint of urine collection. Creatinine clearance is calculated from (1) concentration of creatinine in urine in mg/ml (U), (2) volume of urine excreted in ml/min (V) (this is calculated by the formula: volume of urine collected/collection time in minutes e.g. volume of urine collected in 24 hours ÷ 1440), and (3) concentration of creatinine in plasma in mg/dl (P). Creatinine clearance in ml/min per 1.73 m2 is then derived from the formula UV/P.
 
Because of secretion of creatinine by renal tubules, the above formula overestimates GFR by about 10%. In advanced renal failure, secretion of creatinine by tubules is increased and thus overestimation of GFR is even more.
 
Jaffe’s reaction (see serum creatinine) used for estimation of creatinine measures creatinine as well as some other substances (non-creatinine chromogens) in blood and thus gives slightly higher result. Thus effect of tubular secretion of creatinine is somewhat balanced by slight overestimation of serum creatinine by Jaffe’s reaction.
 
To provide values closer to the actual GFR, cimetidine (which blocks secretion by renal tubules) can be administered before commencing urine collection (cimetidine-enhanced creatinine clearance).
 
Creatinine clearance is not an ideal test for estimation of GFR because of following reasons:
 
  1. A small amount of creatinine is secreted by renal tubules that increase even further in advanced renal failure.
  2. Collection of urine is often incomplete.
  3. Creatinine level is affected by intake of meat and muscle mass.
  4. Creatinine level is affected by certain drugs like cimetidine, probenecid, and trimethoprim (which block tubular secretion of creatinine).
 
Urea Clearance
 
Urea is filtered by the glomeruli, but about 40% of the filtered amount is reabsorbed by the tubules. The reabsorption depends on the rate of urine flow. Thus it underestimates GFR, depends on the urine flow rate, and is not a sensitive indicator of GFR.
 
BUN and serum creatinine, by themselves, are not sensitive indicators of early renal impairment since values may be normal e.g. if baseline values of serum creatinine is 0.5 mg/dl, then 50% reduction in kidney function would increase it to 1.0 mg/dl. Thus clearance tests are more helpful in early cases. If biochemical tests are normal and renal function impairment is suspected, then creatinine clearance test should be carried out. If biochemical tests are abnormal, then clearance tests need not be done.
 
Further Reading:
 
Renal biopsy refers to obtaining a small piece of kidney tissue for microscopic examination. Percutaneous renal biopsy was first performed by Alwall in 1944. In renal disease, renal biopsy is helpful to:
 
  • Establish the diagnosis
  • Assess severity and activity of disease
  • Assess prognosis by noting the amount of scarring
  • To plan treatment and monitor response to therapy
 
Renal biopsy is associated with the risk of procedure-related morbidity and rarely mortality. Therefore, before performing renal biopsy, risks of the procedure and benefits of histologic examination should be evaluated in each patient.
 
Indications for Renal Biopsy
 
  1. Nephrotic syndrome in adults (most common indication)
  2. Nephrotic syndrome not responding to corticosteroids in children.
  3. Acute nephritic syndrome for differential diagnosis
  4. Unexplained renal insufficiency with near-normal kidney dimensions on ultrasonography
  5. Asymptomatic hematuria, when other diagnostic tests fail to identify the source of bleeding
  6. Isolated non-nephrotic range proteinuria (1-3 gm/24 hours) with renal impairment
  7. Impaired function of renal graft
  8. Involvement of kidney in systemic disease like systemic lupus erythematosus or amyloidosis
 
Contraindications
 
  1. Uncontrolled severe hypertension
  2. Hemorrhagic diathesis
  3. Solitary kidney
  4. Renal neoplasm (to avoid spread of malignant cells along the needle track)
  5. Large and multiple renal cysts
  6. Small, shrunken kidneys
  7. Acute urinary tract infection like pyelonephritis
  8. Urinary tract obstruction
 
Complications
 
  1. Hemorrhage: As renal cortex is highly vascular, major risk is bleeding in the form of hematuria or perinephric hematoma. Severe bleeding may occasionally necessitate blood transfusion and rarely removal of kidney.
  2. Arteriovenous fistula
  3. Infection
  4. Accidental biopsy of another organ or perforation of viscus (liver, spleen, pancreas, adrenals, intestine, or gallbladder)
  5. Death (rare).
 
Procedure
 
  1. Patient’s informed consent is obtained.
  2. Ultrasound/CT scan is done to document the location and size of kidneys.
  3. Blood pressure should be less than 160/90 mm of Hg. Bleeding time, platelet count, prothrombin time, and activated partial thromboplastin time should be normal. Blood sample should be drawn for blood grouping and cross matching, as blood transfusion may be needed.
  4. Patient is sedated before the procedure.
  5. Patient lies in prone position and kidney is identified with ultrasound.
  6. The skin over the selected site is disinfected and a local anesthetic is infiltrated.
  7. A small skin incision is given with a scalpel (to insert the biopsy needle). Localization of kidney is done with a fine bore 21 G lumbar puncture needle. A local anesthetic is infiltrated down to the renal capsule.
  8. A tru-cut biopsy needle or spring loaded biopsy gun is inserted under ultrasound guidance and advanced down to the lower pole. Biopsy is usually obtained from lateral border of lower pole. Patient should hold his/her breath in full inspiration during biopsy. After obtaining the biopsy and removal of needle, patient is allowed to breath normally.
  9. The biopsy should be placed in a drop of saline and examined under a dissecting microscope for adequacy.
  10. Patient is turned to supine position. Vital signs and appearance of urine should be monitored at regular intervals. Patient is usually kept in the hospital for 24 hours.
 
Kidney biopsy can be divided into three parts for light microscopy, immunofluorescence, and electron microscopy. For light microscopy, renal biopsy is routinely fixed in neutral buffered formaldehyde. Sections are stained by:
 
  • Hematoxylin and eosin (for general architecture of kidney and cellularity)
  • Periodic acid Schiff: To highlight basement membrane and connective tissue matrix.
  • Congo red: For amyloid.
 
For electron microscopy, tissue is fixed in glutaraldeyde. In immunohistochemistry, tissue deposits of IgG, IgA, IgM, C3, fibrin, and κ and λ light chains can be detected by using appropriate antibodies. Many kidney diseases are immune-complex mediated.

In DM, applications of laboratory tests are as follows:

  • Diagnosis of DM
  • Screening of DM
  • Assessment of glycemic control
  • Assessment of associated long-term risks
  • Management of acute metabolic complications.

LABORATORY TESTS FOR DIAGNOSIS OF DIABETES MELLITUS

Diagnosis of DM is based exclusively on demonstration of raised blood glucose level (hyperglycemia).

The current criteria (American Diabetes Association, 2004) for diagnosis of DM are as follows:

Typical symptoms of DM (polyuria, polydipsia, weight loss) and random plasma glucose ≥ 200 mg/dl (≥ 11.1 mmol/L)

article continued below

Or

Fasting plasma glucose ≥ 126 mg/dl (≥ 7.0 mmol/L)

Or

2-hour post glucose load (75 g) value during oral glucose tolerance test ≥ 200 mg/dl (≥ 11.1 mmol/L).

If any one of the above three criteria is present, confirmation by repeat testing on a subsequent day is necessary for establishing the diagnosis of DM. However, such confirmation by repeat testing is not required if patient presents with (a) hyperglycemia and ketoacidosis, or (b) hyperosmolar hyperglycemia.

The tests used for laboratory diagnosis of DM are (1) estimation of blood glucose and (2) oral glucose tolerance test.

Estimation of Blood Glucose

Measurement of blood glucose level is a simple test to assess carbohydrate metabolism in DM (Figure 837.1). Since glucose is rapidly metabolized in the body, measurement of blood glucose is indicative of current state of carbohydrate metabolism.

Figure 837.1 Blood glucose values in normal individuals
Figure 837.1 Blood glucose values in normal individuals, prediabetes, and diabetes mellitus

Glucose concentration can be estimated in whole blood (capillary or venous blood), plasma or serum. However, concentration of blood glucose differs according to nature of the blood specimen. Plasma glucose is about 15% higher than whole blood glucose (the figure is variable with hematocrit). During fasting state, glucose levels in both capillary and venous blood are about the same. However, postprandial or post glucose load values are higher by 20-70 mg/dl in capillary blood than venous blood. This is because venous blood is on a return trip after delivering blood to the tissues.

When whole blood is left at room temperature after collection, glycolysis reduces glucose level at the rate of about 7 mg/dl/hour. Glycolysis is further increased in the presence of bacterial contamination or leucocytosis. Addition of sodium fluoride (2.5 mg/ml of blood) maintains stable glucose level by inhibiting glycolysis. Sodium fluoride is commonly used along with an anticoagulant such as potassium oxalate or EDTA. Addition of sodium fluoride is not necessary if plasma is separated from whole blood within 1 hour of blood collection.

Plasma is preferred for estimation of glucose since whole blood glucose is affected also by concentration of proteins (especially hemoglobin).

There are various methods for estimation of blood glucose:

  • Chemical methods:
    – Orthotoluidine method
    – Blood glucose reduction methods using neocuproine, ferricyanide, or copper.

Chemical methods are less specific but are cheaper as compared to enzymatic methods.

  • Enzymatic methods: These are specific for glucose.
    – Glucose oxidase-peroxidase
    – Hexokinase
    – Glucose dehydrogenase

Chemical methods have now been replaced by enzymatic methods.

Terms used for blood glucose specimens: Depending on the time of collection, different terms are used for blood glucose specimens.

  • Fasting blood glucose: Sample for blood glucose is withdrawn after an overnight fast (no caloric intake for at least 8 hours).
  • Post meal or postprandial blood glucose: Blood sample for glucose estimation is collected 2 hours after the subject has taken a normal meal.
  • Random blood glucose: Blood sample is collected at any time of the day, without attention to the time of last food intake.

Oral Glucose Tolerance Test (OGTT)

Glucose tolerance refers to the ability of the body to metabolize glucose. In DM, this ability is impaired or lost and glucose intolerance represents the fundamental pathophysiological defect in DM. OGTT is a provocative test to assess response to glucose challenge in an individual (Figure 837.2).

Figure 837.2 Oral glucose tolerance curve
Figure 837.2 Oral glucose tolerance curve

American Diabetes Association does not recommend OGTT for routine diagnosis of type 1 or type 2 DM. This is because fasting plasma glucose cutoff value of 126 mg/dl identifies the same prevalence of abnormal glucose metabolism in the population as OGTT. World Health Organization (WHO) recommends OGTT in those cases in which fasting plasma glucose is in the range of impaired fasting glucose (i.e. 100-125 mg/dl). Both ADA and WHO recommend OGTT for diagnosis of gestational diabetes mellitus.

Preparation of the Patient

  • Patient should be put on a carbohydrate-rich, unrestricted diet for 3 days. This is because carbohydrate-restricted diet reduces glucose tolerance.
  • Patient should be ambulatory with normal physical activity. Absolute bed rest for a few days impairs glucose tolerance.
  • Medications should be discontinued on the day of testing.
  • Exercise, smoking, and tea or coffee are not allowed during the test period. Patient should remain seated.
  • OGTT is carried out in the morning after patient has fasted overnight for 8-14 hours.

Test

  1. A fasting venous blood sample is collected in the morning.
  2. Patient ingests 75 g of anhydrous glucose in 250-300 ml of water over 5 minutes. (For children, the dose is 1.75 g of glucose per kg of body weight up to maximum 75 g of glucose). Time of starting glucose drink is taken as 0 hour.
  3. A single venous blood sample is collected 2 hours after the glucose load. (Previously, blood samples were collected at ½, 1, 1½, and 2 hours, which is no longer recommended).
  4. Plasma glucose is estimated in fasting and 2-hour venous blood samples.

Interpretation of blood glucose levels is given in Table 837.1.

Table 837.1 Interpretation of oral glucose tolerance test
Parameter Normal Impaired fasting glucose Impaired glucose tolerance Diabetes mellitus
(1) Fasting (8 hr) < 100 100-125 ≥ 126
(2) 2 hr OGTT < 140 < 140 140-199 ≥ 200

OGTT in gestational diabetes mellitus: Impairment of glucose tolerance develops normally during pregnancy, particularly in 2nd and 3rd trimesters. Following are the recent guidelines of ADA for laboratory diagnosis of GDM:

  • Low-risk pregnant women need not be tested if all of the following criteria are met, i.e. age below 25 years, normal body weight (before pregnancy), absence of diabetes in first-degree relatives, member of an ethnic group with low prevalence of DM, no history of poor obstetric outcome, and no history of abnormal glucose tolerance.
  • Average-risk pregnant women (i.e. who are in between low and high risk) should be tested at 24-28 weeks of gestation.
  • High-risk pregnant women i.e. those who meet any one of the following criteria should be tested immediately: marked obesity, strong family history of DM, glycosuria, or personal history of GDM.

Initially, fasting plasma glucose or random plasma glucose should be obtained. If fasting plasma glucose is ≥ 126 mg/dl or random plasma glucose is ≥ 200 mg/dl, repeat testing should be carried out on a subsequent day for confirmation of DM. If both the tests are normal, then OGTT is indicated in average-risk and high-risk pregnant women.

There are two approaches for laboratory diagnosis of GDM

  • One step approach
  • Two step approach

In one step approach, 100 gm of glucose is administered to the patient and a 3-hour OGTT is performed. This test may be cost-effective in high-risk pregnant women.

In two-step approach, an initial screening test is done in which patient drinks a 50 g glucose drink irrespective of time of last meal and a venous blood sample is collected 1 hour later (O’Sullivan’s test). GDM is excluded if glucose level in venous plasma sample is below 140 mg/dl. If level exceeds 140 mg/dl, then the complete 100 g, 3-hour OGTT is carried out.

In the 3-hour OGTT, blood samples are collected in the morning (after 8-10 hours of overnight fasting), and after drinking 100 g glucose, at 1, 2, and 3 hours. For diagnosis of GDM, glucose concentration should be above the following cut-off values in 2 or more of the venous plasma samples:

  • Fasting: 95 mg/dl
  • 1 hour: 180 mg/dl
  • 2 hour: 155 mg/dl
  • 3 hour: 140 mg/dl

LABORATORY TESTS FOR SCREENING OF DIABETES MELLITUS

Aim of screening is to identify asymptomatic individuals who are likely to have DM. Since early detection and prompt institution of treatment can reduce subsequent complications of DM, screening may be an appropriate step in some situations.

Screening for type 2 DM: Type 2 DM is the most common type of DM and is usually asymptomatic in its initial stages. Its onset occurs about 5-7 years before clinical diagnosis. Evidence indicates that complications of type 2 DM begin many years before clinical diagnosis. American Diabetes Association recommends screening for type 2 DM in all asymptomatic individuals ≥ 45 years of age using fasting plasma glucose. If fasting plasma glucose is normal (i.e. < 100 mg/dl), screening test should be repeated every three years.

Another approach is selective screening i.e. screening individuals at high risk of developing type 2 DM i.e. if one or more of the following risk factors are presentobesity (body mass index ≥ 25.0 kg/m2), family history of DM (first degree relative with DM), high-risk ethnic group, hypertension, dyslipidemia, impaired fasting glucose, impaired glucose tolerance, or history of GDM. In such cases, screening is performed at an earlier age (30 years) and repeated more frequently.

Recommended screening test for type 2 DM is fasting plasma glucose. If ≥126 mg/dl, it should be repeated on a subsequent day for confirmation of diagnosis. If <126 mg/dl, OGTT is indicated if clinical suspicion is strong. A 2-hour post-glucose load value in OGTT ≥200 mg/dl is indicative of DM and should be repeated on a different day for confirmation.

Screening for type 1 DM: Type 1 DM is detected early after its onset since it has an acute presentation with characteristic clinical features. Therefore, it is not necessary to screen for type 1 DM by estimation of blood glucose. Detection of immunologic markers (mentioned earlier) has not been recommended to identify persons at risk.

Screening for GDM: Given earlier under OGTT in gestational diabetes mellitus.

LABORATORY TESTS TO ASSESS GLYCEMIC CONTROL

There is a direct correlation between the degree of blood glucose control in DM (both type 1 and type 2) and the development of microangiopathic complications i.e. nephropathy, retinopathy, and neuropathy. Maintenance of blood glucose level as close to normal as possible (referred to as tight glycemic control) reduces the risk of microvascular complications. There is also association between persistently high blood glucose values in DM with increased cardiovascular mortality.

Following methods can monitor degree of glycemic control:

  • Periodic measurement of glycated hemoglobin (to assess long-term control).
  • Daily self-assessment of blood glucose (to assess day-to- day or immediate control).

Glycated Hemoglobin (Glycosylated Hemoglobin, HbA1C)

Glycated hemoglobin refers to hemoglobin to which glucose is attached nonenzymatically and irreversibly; its amount depends upon blood glucose level and lifespan of red cells.

Hemoglobin + Glucose ↔ Aldimine → Glycated hemoglobin

Plasma glucose readily moves across the red cell membranes and is being continuously combined with hemoglobin during the lifespan of the red cells (120 days). Therefore, some hemoglobin in red cells is present normally in glycated form. Amount of glycated hemoglobin in blood depends on blood glucose concentration and lifespan of red cells. If blood glucose concentration is high, more hemoglobin is glycated. Once formed, glycated hemoglobin is irreversible. Level of glycated hemoglobin is proportional to the average glucose level over preceding 6-8 weeks (about 2 months). Glycated hemoglobin is expressed as a percentage of total hemoglobin. Normally, less than 5% of hemoglobin is glycated.

Numerous prospective studies have demonstrated that a good control of blood glucose reduces the development and progression of microvascular complications (retinopathy, nephropathy, and peripheral neuropathy) of diabetes mellitus. Mean glycated hemoglobin level correlates with the risk of these complications.

The terms glycated hemoglobin, glycosylated hemoglobin, glycohemoglobin, HbA1, and HbA1c are often used interchangeably in practice. Although these terms refer to hemoglobins that contain nonenzymatically added glucose residues, hemoglobins thus modified differ. Most of the studies have been carried out with HbA1c.

Glycated hemoglobin should be routinely measured in all diabetic patients (both type 1 and type 2) at regular intervals to assess degree of long-term glycemic control. Apart from mean glycemia (over preceding 120 days), glycated hemoglobin level also correlates with the risk of the development of chronic complications of DM. In DM, it is recommended to maintain glycated hemoglobin level to less than 7%.

Box 837.1 Glycated hemoglobin 
  • Hemoglobin A1C of 6% corresponds to mean serum glucose level of 135 mg/dl. With every rise of 1%, serum glucose increases by 35 mg/dl. Approximations are as follows:
    – Hb A1C 7%: 170 mg/dl
    – Hb A1C 8%: 205 mg/dl
    – Hb A1C 9%: 240 mg/dl
    – Hb A1C 10%: 275 mg/dl
    – Hb A1C 11%: 310 mg/dl
    – Hb A1C 12%: 345 mg/dl
  • Assesses long-term control of DM (thus indirectly confirming plasma glucose results or self-testing results).
  • Assesses whether treatment plan is working
  • Measurement of glycated hemoglobin does not replace measurement of day-to-day control by glucometer devices.

Spurious results of glycated hemoglobin are seen in reduced red cell survival (hemolysis), blood loss, and hemoglobinopathies.

In DM, if glycated hemoglobin is less than 7%, it should be measured every 6 months. If >8%, then more frequent measurements (every 3 months) along with change in treatment are advocated.

There are various methods for measurement of glycated hemoglobin such as chromatography, immunoassay, and agar gel electrophoresis.

Role of glycated hemoglobin in management of DM is highlighted in Box 837.1.

Self-Monitoring of Blood Glucose (SMBG)

Diabetic patients are taught how to regularly monitor their own blood glucose levels. Regular use of SMBG devices (portable glucose meters) by diabetic patients has improved the management of DM. With SMBG devices, blood glucose level can be monitored on day-to-day basis and kept as close to normal as possible by adjusting insulin dosage. SMBG devices measure capillary whole blood glucose obtained by fingerprick and use test strips that incorporate glucose oxidase or hexokinase. In some strips, a layer is incorporated to exclude blood cells so that glucose in plasma is measured. Aim of achieving tight glycemic control introduces the risk of severe hypoglycemia. Daily use of SMBG devices can avoid major hypoglycemic episodes.

SMBG devices yield unreliable results at very high and very low glucose levels. It is necessary to periodically check the performance of the glucometer by measuring parallel venous plasma glucose in the laboratory.

Portable glucose meters are used by patients for day-to-day self-monitoring, by physicians in their OPD clinics, and by health care workers for monitoring admitted patients at the bedside. These devices should not be used for diagnosis and population screening of DM as they lack precision and there is variability of results between different meters.

Goal of tight glycemic control in type 1 DM patients on insulin can be achieved through self-monitoring of blood glucose by portable blood glucose meters.

Glycosuria

Semiquantitative urine glucose testing for monitoring of diabetes mellitus in home setting is not recommended. This is because (1) even if glucose is absent in urine, no information about blood glucose concentration below the renal threshold (which itself is variable) is obtained (Normally, renal threshold is around 180 mg/dl; it tends to be lower in pregnancy (140 mg/dl) and higher in old age and in long-standing diabetics; in some normal persons it is low), (2) urinary glucose testing cannot detect hypoglycemia, and (3) concentration of glucose in urine is affected by urinary concentration. Semiquantitative urine glucose testing for monitoring has now been replaced by self-testing by portable glucose meters.

LABORATORY TESTS TO ASSESS LONG-TERM RISKS

Urinary Albumin Excretion
 
Diabetes mellitus is one of the leading causes of renal failure. Diabetic nephropathy develops in around 20-30% of patients with type 1 or type 2 DM. Diabetic nephropathy progresses through different stages as shown in Figure 837.3. Hypertension also develops along the course of nephropathy with increasing albumin excretion. Evidence indicates that if diabetic nephropathy is detected early and specific treatment is instituted, further progression of nephropathy can be significantly ameliorated. Early detection of diabetic nephropathy is based on estimation of urinary albumin excretion. In all adult patients with DM, usual reagent strip test for proteinuria should be carried out periodically. Positive test means presence of overt proteinuria or clinical proteinuria and may be indicative of overt nephropathy. In all such patients quantitation of albuminuria should be carried out to plan appropriate therapy. If the routine dipstick test for proteinuria is negative, test for microalbuminuria should be carried out.
 
Figure 837.3 Evolution of diabetic nephropathy
Figure 837.3 Evolution of diabetic nephropathy. In 80% of patients with type 1 DM, microalbuminuria progresses in 10-15 years to overt nephropathy that is then followed in majority of cases by progressive fall in GFR and ultimately end-stage renal disease. Amongst patients with type 2 DM and microalbuminuria, 20-40% of patients progress to overt nephropathy, and about 20% of patients with overt nephropathy develop end-stage renal disease. Abbreviation: GFR: Glomerular filtration rate
 
The term ‘microalbuminuria’ refers to the urinary excretion of albumin below the level of detection by routine dipstick testing but above normal (30-300 mg/ 24 hrs, 20-200 μg/min, or 30-300 μg/mg of creatinine). Albumin excretion rate is intermediate between normal (normal albumin excretion in urine is < 30 mg/24 hours) and overt albuminuria (> 300 mg/24 hours). Significance of microalbuminuria in DM is as follows:
 
  • It is the earliest marker of diabetic nephropathy. Early diabetic nephropathy is reversible.
  • It is a risk factor for cardiovascular disease in both type 1 and type 2 patients.
  • It is associated with higher blood pressure and poor glycemic control.
 
Specific therapeutic interventions such as tight glycemic control, administration of ACE (angiotensinconverting enzyme) inhibitors, and aggressive treatment of hypertension significantly slow down the progression of diabetic nephropathy.
 
In type 2 DM, screening for microalbuminuria should begin at the time of diagnosis, whereas in type 1 DM, it should begin 5 years after diagnosis. At this time, a routine reagent strip test for proteinuria is carried out; if negative, testing for microalbuminuria is done. Thereafter, in all patients who test negative, screening for microalbuminuria should be repeated every year.
 
Screening tests for microalbuminuria include:
 
 
Reagent strip tests to detect microalbuminuria are available. Positive results should be confirmed by more specific quantitative tests like radioimmunoassay and enzyme immunoassay. For diagnosis of microalbuminuria, tests should be positive in at least two out of three different samples over a 3 to 6 month period.
 
Lipid Profile
 
Abnormalities of lipids are associated with increased risk of coronary artery disease (CAD) in patients with DM. This risk can be reduced by intensive treatment of lipid abnormalities. Lipid parameters which should be measured include:
 
  • Total cholesterol
  • Triglycerides
  • Low-density lipoprotein (LDL) cholesterol
  • High-density lipoprotein (HDL) cholesterol
 
The usual pattern of lipid abnormalities in type 2 DM is elevated triglycerides, decreased HDL cholesterol and higher proportion of small, dense LDL particles. Patients with DM are categorized into high, intermediate and low-risk categories depending on lipid levels in blood (Table 837.2).
 
Table 837.2 Categorization of cardiovascular risk in diabetes mellitus according to lipid levels (American Diabetes Association)
Category Low density lipoproteins High density lipoproteins Triglycerides
High-risk ≥130 < 35 (men) ≥ 400
    < 45 (women)  
Intermediate risk 100-129 35-45 200-399
Low-risk < 100 > 45 (men) < 200
    > 55 (women)  
 
Annual lipid profile is indicated in all adult patients with DM.
 
LABORATORY TESTS IN THE MANAGEMENT OF ACUTE METABOLIC COMPLICATIONS OF DIABETES MELLITUS
 
The three most serious acute metabolic complications of DM are:
 
  • Diabetic ketoacidosis (DKA)
  • Hyperosmolar hyperglycemic state (HHS)
  • Hypoglycemia
 
The typical features of DKA are hyperglycemia, ketosis, and acidosis. The common causes of DKA are infection, noncompliance with insulin therapy, alcohol abuse and myocardial infarction. Patients with DKA present with rapid onset of polyuria, polydipsia, polyphagia, weakness, vomiting, and sometimes abdominal pain. Signs include Kussmaul’s respiration, odour of acetone on breath (fruity), mental clouding, and dehydration. Classically, DKA occurs in type 1, while HHS is more typical of type 2 DM. However, both complications can occur in either types. If untreated, both events can lead to coma and death.
 
Hyperosmolar hyperglycemic state is characterized by very high blood glucose level (> 600 mg/dl), hyperosmolality (>320 mOsmol/kg of water), dehydration, lack of ketoacidosis, and altered mental status. It usually occurs in elderly type 2 diabetics. Insulin secretion is adequate to prevent ketosis but not hyperglycemia. Causes of HHS are illness, dehydration, surgery, and glucocorticoid therapy.
 
Differences between DKA and HHS are presented in Table 837.3.
 
Table 837.3 Comparison of diabetic ketoacidosis and hyperosmolar hyperglycemic state
Parameter Diabetic ketoacidosis Hyperosmolar hyperglycemic state
1. Type of DM in which more common  Type 1 Type 2 
2. Age  Younger age  Older age
3. Prodromal clinical features  < 24 hrs  Several days
4. Abdominal pain, Kussmaul’s respiration  Yes  No
5. Acidosis  Moderate/Severe  Absent
6. Plasma glucose  > 250 mg/dl  Very high (>600 mg/dl)
7. Serum bicarbonate  <15 mEq/L  >15 mEq/L
8. Blood/urine ketones  ++++  ±
9. β-hydroxybutyrate  High  Normal or raised
10. Arterial blood pH  Low (<7.30)  Normal (>7.30)
11. Effective serum osmolality*  Variable  Increased (>320)
12. Anion gap**  >12  Variable
Osmolality: Number of dissolved (solute) particles in solution; normal: 275-295 mOsmol/kg
** Anion gap: Difference between sodium and sum of chloride and bicarbonate in plasma; normal average value is 12
 
Laboratory evaluation consists of following investigations:
 
  • Blood and urine glucose
  • Blood and urine ketone
  • Arterial pH, Blood gases
  • Serum electrolytes (sodium, potassium, chloride, bicarbonate)
  • Blood osmolality
  • Serum creatinine and blood urea.
 
Testing for ketone bodies: Ketone bodies are formed from metabolism of free fatty acids and include acetoacetic acid, acetone and β-hydroxybutyric acid.
 
Indications for testing for ketone bodies in DM include:
 
  • At diagnosis of diabetes mellitus
  • At regular intervals in all known cases of diabetes, during pregnancy with pre-existing diabetes, and in gestational diabetes
  • In known diabetic patients: during acute illness, persistent hyperglycemia (> 300 mgs/dl), pregnancy, and clinical evidence of diabetic acidosis (nausea, vomiting, abdominal pain).
 
An increased amount of ketone bodies in patients with DM indicate impending or established diabetic ketoacidosis and is a medical emergency. Method based on colorimetric reaction between ketone bodies and nitroprusside (by dipstick or tablet) is used for detection of both blood and urine ketones.
 
Test for urine ketones alone should not be used for diagnosis and monitoring of diabetic ketoacidosis. It is recommended to measure β-hydroxybutyric acid (which accounts for 75% of all ketones in ketoacidosis) for diagnosis and monitoring DKA.
 
REFERENCE RANGES
 
  • Venous plasma glucose:
    Fasting: 60-100 mg/dl
    At 2 hours in OGTT (75 gm glucose): <140 mg/dl
  • Glycated hemoglobin: 4-6% of total hemoglobin
  • Lipid profile:
    – Serum cholesterol: Desirable level: <200 mg/dl
    – Serum triglycerides: Desirable level: <150 mg/dl
    – HDL cholesterol: ≥60 mg/dl
    – LDL cholesterol: <130 mg/dl
    – LDL/HDL ratio: 0.5-3.0
  • C-peptide: 0.78-1.89 ng/ml
  • Arterial pH: 7.35-7.45
  • Serum or plasma osmolality: 275-295 mOsm/kg of water.

Serum Osmolality can also be calculated by the following formula recommended by American Diabetes Association:
 
Effective serum osmolality (mOsm/kg) = (2 × sodium mEq/L) + Plasma glucose (mg/dl)
                                                                                                            18
 
  • Anion gap:
    – Na+ – (Cl + HCO3): 8-16 mmol/L (Average 12)
    – (Na+ + K+) – (Cl + HCO3): 10-20 mmol/L (Average 16)
  • Serum sodium: 135-145 mEq/L
  • Serum potassium: 3.5-5.0 mEq/L
  • Serum chloride: 100-108 mEq/L
  • Serum bicarbonate: 24-30 mEq/L
 
CRITICAL VALUES
 
  • Venous plasma glucose: > 450 mg/dl
  • Strongly positive test for glucose and ketones in urine
  • Arterial pH: < 7.2 or > 7.6
  • Serum sodium: < 120 mEq/L or > 160 mEq/L
  • Serum potassium: < 2.8 mEq/L or > 6.2 mEq/L
  • Serum bicarbonate: < 10 mEq/L or > 40 mEq/L
  • Serum chloride: < 80 mEq/L or > 115 mEq/L

PREGNANCY TESTS

  • 16 Aug 2017

Pregnancy tests detect human chorionic gonadotropin (hCG) in serum or urine. Although pregnancy is the most common reason for ordering the test for hCG, measurement of hCG is also indicated in other conditions as shown in Box 836.1.

Human chorionic gonadotropin is a glycoprotein hormone produced by placenta that circulates in maternal blood and excreted intact by the kidneys. It consists of two polypeptide subunits: α (92 amino acids) and β (145 amino acids) which are non-covalently bound to each other. Structurally, hCG is closely related to three other glycoprotein hormones, namely, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). The α subunits of hCG, LH, FSH, and TSH are similar, while β subunits differ and confer specific biologic and immunologic properties. Immunological tests use antibodies directed against β-subunit of hCG to avoid cross-reactivity against LH, FSH, and TSH.

Box 836.1 Indications for measurement of β human chorionic gonadotropin

• Early diagnosis of pregnancy
• Diagnosis and management of gestational trophoblastic disease
• As a part of maternal triple test screen
• Follow-up of malignant tumors that produce β human chorionic gonadotropin.

Syncytiotrophoblastic cells of conceptus and later of placenta synthesize hCG. Human chorionic gonadotropin supports the corpus luteum of ovary during early pregnancy. Progesterone, produced by corpus luteum, prevents ovulation and thus maintains pregnancy. After 7-10 weeks of gestation, sufficient amounts of progesterone are synthesized by placenta, and hCG is no longer needed and its level declines.

CLINICAL APPLICATIONS OF TESTS FOR HUMAN CHORIONIC GONADOTROPIN

  1. Early diagnosis of pregnancy: Qualitative serum hCG test becomes positive 3 weeks after last menstrual period (LMP), while urine hCG test becomes positive 5 weeks after LMP.
  2. Exclusion of pregnancy before prescribing certain medications (like oral contraceptives, steroids, some antibiotics), and before ordering radiological studies, radiotherapy, or chemotherapy. This is necessary to prevent any teratogenic effect on the fetus.
  3. Early diagnosis of ectopic pregnancy: Trans-vaginal ultrasonography (USG) and quantitative estimation of hCG are helpful in early diagnosis of ectopic pregnancy (before rupture).
  4. Evaluation of threatened abortion: Serial quantitative estimation of hCG is helpful in following the course of threatened abortion.
  5. Diagnosis and follow-up of gestational trophoblastic disease (GTD).
  6. Maternal triple test screen: This consists of measurement of hCG, α-fetoprotein, and unconjugated estriol in maternal serum at 14-19 weeks of gestation. The maternal triple screen identifies pregnant women with increased risk of Down syndrome and major congenital anomalies like neural tube defects.
  7. Follow-up of ovarian or testicular germ cell tumors, which produce hCG.

Normal Pregnancy

In women with normal menstrual cycle, conception (fertilization of ovum to form a zygote) occurs on day 14 in the fallopian tube. Zygote travels down the fallopian tube into the uterus. Division of zygote produces a morula. At 50-60-cell stage, morula develops a primitive yolk sac and is then called as a blastocyst. About 5 days after fertilization, implantation of blastocyst occurs in the uterine wall. Trophoblastic cells (on the outer surface of the blastocyst) penetrate the endometrium and develop into chorionic villi. There are two main forms of trophoblasts—syncytiotrophoblast and cytotrophoblast. Placental development occurs from chorionic villi. After formation of placenta, the conceptus is called as an embryo. When embryo develops most major organs, it is called as fetus (after 10 weeks of gestation).

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Figure 836.1 Level of human chorionic gonadotropin during pregnancy
Figure 836.1Level of human chorionic gonadotropin during pregnancy

Box 836.2 Diagnosis of early pregnancy

• Positive serum hCG test: 8 days after conception or 3 weeks after last menstrual period (LMP)
• Positive urine hCG test: 21 days after conception or 5 weeks after LMP
• Ultrasonography for visualization of gestational sac:
– Transvaginal: 21 days after conception or 5 weeks after LMP
– Transabdominal: 28 days after conception or 6 weeks after LMP

Human chorionic gonadotropin is synthesized by syncytiotrophoblasts (of placenta) and detectable amounts (~5 mIU/ml) appear in maternal serum about 8 days after conception (3 weeks after LMP). In the first trimester (first 12 weeks, calculated from day 1 of LMP) of pregnancy, hCG levels rapidly rise with a doubling time of about 2 days. Highest or peak level is reached at 8-10 weeks (about 100,000 mIU/ml). This is followed by a gradual fall, and from 15-16 weeks onwards, a steady level of 10,000-20,000 mIU/ml is maintained for the rest of the pregnancy (Figure 836.1). After delivery, hCG becomes non-detectable by about 2 weeks.

Box 836.2 shows minimum time required for the earliest diagnosis of pregnancy by hCG test and ultrasonography (USG).

Two types of pregnancy tests are available:

  • Qualitative tests: These are positive/negative result types that are done on urine sample.
  • Quantitative tests: These give numerical result and are done on serum or urine. They are also used for evaluation of ectopic pregnancy, failing pregnancy, and for follow-up of gestational trophoblastic disease.

Ectopic Pregnancy

Ectopic pregnancy refers to the implantation of blastocyst at a site other than the cavity of uterus. The most common of such sites (>95% cases) is fallopian tube. Early diagnosis and treatment of tubal ectopic pregnancy is essential since it can lead to maternal mortality (from rupture and hemorrhage) and future infertility. Ectopic pregnancy is a leading cause of maternal death during first trimester. Diagnosis of ectopic pregnancy can be readily made in most cases by ultrasonography and estimation of β-subunit of human chorionic gonadotropin.

Early diagnosis of unruptured tubal pregnancy can be made by quantitative estimation of serum hCG and ultrasonography. In normal intrauterine pregnancy, hCG titer doubles every 2 days until first 40 days of gestation. If hCG rise is abnormally slow, then an unviable pregnancy (either ectopic or abnormal intrauterine pregnancy) should be suspected.

Transabdominal USG can detect gestational sac in intrauterine pregnancy 6 weeks after LMP. The level of hCG in serum at this stage is >6500 mIU/ml. If gestational sac is not visualized at this level of hCG, then there is a possibility of ectopic pregnancy. Transvaginal ultrasonography can detect ectopic pregnancy average 1 week earlier than abdominal ultrasonography; it can detect gestational sac if β-hCG level is 1000-1500 mIU/ml. Therefore, if gestational sac is not visualized in the presence of >1500 mIU/ml of β-hCG level, an ectopic pregnancy can be suspected.

Early diagnosis of ectopic pregnancy provides the option of administration of intramuscular methotrexate (rather than surgery), which causes dissolution of conceptus. This improves the chances of patient’s future fertility. Serial measurements of hCG after surgical removal of ectopic pregnancy can help in detecting persistence of trophoblastic tissue.

Abortion

Termination of pregnancy before fetus becomes viable (i.e. before 20 weeks) is called as abortion.

In threatened abortion, vaginal bleeding is present but internal os is closed and process of abortion, though started, is still reversible. It is possible that pregnancy will continue.

Serial quantitative titers of hCG showing lack of expected doubling of hCG level and USG are helpful in diagnosis and management of abortion.

Gestational Trophoblastic Disease (GTD)

It is characterized by proliferation of pregnancyassociated trophoblastic tissue. The two main forms of GTD are hydatidiform (vesicular) mole (benign) and choriocarcinoma (malignant). Clinical features of GTD are as follows:

  • Short history of amenorrhea followed by vaginal bleeding.
  • Size of uterus larger than gestational age; uterus is soft and doughy on palpation with no fetal parts and no fetal heart sounds.
  • Excessive nausea and vomiting due to high hCG.
  • Characteristic snowstorm appearance on pelvic USG.

Quantitative estimation of hCG is helpful in diagnosis and management of GTD.

Trophoblastic cells of GTD produce more hCG as compared to the trophoblasts of normal pregnancy for the same gestational age. Concentration of hCG parallels tumor load. Also, hCG continues to rise beyond 10 weeks of gestation without reaching plateau (as expected at the end of first trimester).

After evacuation of uterus, weekly estimation of hCG is advised till subsequent three (weekly) results are negative; following evacuation of vesicular mole, hCG becomes undetectable (after 2-3 months) on follow-up in 80% of cases. Plateau or rising hCG indicates persistent GTD. In such cases, chemotherapy is indicated.

Negative results for hCG after therapy should be regularly followed up every 3 months for 1-2 years.

LABORATORY TESTS FOR HUMAN CHORIONIC GONADOTROPIN

These are classified into two main groups:

  • Biological assays or bioassays
  • Immunological assays

Bioassays

In bioassay, effect of hCG is tested on laboratory animals under standardized conditions. There are several limitations of bioassays like need for animal facilities, need for standardization of animals, long time required for the test results, low sensitivity, and high cost. Therefore, bioassays have been replaced by immunological assays.

In Ascheim-Zondek test, urine from pregnant woman is injected into immature female mice. Formation of hemorrhagic corpora lutea in ovaries (after 4 days) is a positive test. Friedman test is similar except that urine is injected into female rabbit. In rapid rat test, injection of urine containing hCG into female rats is followed by hyperaemia and hemorrhage in ovaries. Yet another test measures release of spermatozoa from male frog after injection of urine containing hCG.

Immunological Assays

These are rapid and sensitive tests for detection and quantitation of hCG. Variable results are obtained by different immunological tests with the same serum sample; this is due to differences in specificity of different immunoassays to complete hCG, β-subunit, and β-core fragment. A number of immunological tests are commercially available based on different principles like agglutination inhibition assay, enzyme immunoassay including enzyme linked immunosorbent assay or ELISA, radioimmunoassay (RIA), and immunoradiometric assay.

A commonly used qualitative urine test is agglutination inhibition assay. Early morning urine specimen is preferred because it contains the highest concentration of hCG. Causes of false-positive test include red cells, leukocytes, bacteria, some drugs, proteins, and excess luteinizing hormone (menopause, midcycle LH surge) in urine. Some patients have anti-mouse antibodies (that are used in the test), while others have hCG-like material in circulation, producing false-positive test. Anti-mouse antibodies also interfere with other antibody-based tests and are known as ‘heterophil’ antibodies. Fetal death, abortion, dilute urine, and low sensitivity of a particular test are causes of false-negative test. Renal failure leads to accumulation of interfering substances causing incorrect results.

Figure 836.2 Principle of agglutination inhibition test for diagnosis of pregnancy
Figure 836.2 Principle of agglutination inhibition test for diagnosis of pregnancy

In latex particle agglutination inhibition test (Figure 836.2), anti-hCG antibodies are incubated with patient’s urine. This is followed by addition of hCGcoated latex particles. If hCG is present in urine, anti-hCG serum is neutralized, and no agglutination of latex particles occurs (positive test). If there is no hCG in urine, there is agglutination of latex particles (negative test). This is commonly used as a slide test and requires only a few minutes.

Sensitivity of agglutination inhibition test is >200 units/liter of hCG.

Radioimmunoassay, enzyme immunoassay, and radioimmunometric assay are more sensitive and reliable than agglutination inhibition assay.

Quantitative tests are employed for detection of very early pregnancy, estimation of gestational age, diagnosis of ectopic pregnancy, evaluation of threatened abortion, and management of GTD.

REFERENCE RANGES

  • Serum human chorionic gonadotropin:
    – Non-pregnant females: <5.0 mIU/ml
    – Pregnancy: 4 weeks after LMP: 5-100 mIU/ml
    – 5 weeks after LMP: 200-3000 mIU/ml
    – 6 weeks after LMP: 10,000-80,000 mIU/ml
    – 7-14 weeks: 90,000-500,000 mIU/ml
    – 15-26 weeks: 5000-80000 mIU/ml
    – 27-40 weks: 3000-15000 mIU/ml

Further Reading: SEMEN ANALYSIS FOR INVESTIGATION OF INFERTILITY

 Box 835.1 Contributions to semen volume
 
• Testes and epididymis: 10%
• Seminal vesicles: 50%
• Prostate: 40%
• Cowper’s glands: Small volume
Semen (or seminal fluid) is a fluid that is emitted from the male genital tract and contains sperms that are capable of fertilizing female ova. Structures involved in production of semen are (Box 835.1):
 
  • Testes: Male gametes or spermatozoa (sperms) are produced by testes; constitute 2-5% of semen volume.
  • Epididymis: After emerging from the testes, sperms are stored in the epididymis where they mature; potassium, sodium, and glycerylphosphorylcholine (an energy source for sperms) are secreted by epididymis.
  • Vas deferens: Sperms travel through the vas deferens to the ampulla which is another storage area. Ampulla secretes ergothioneine (a yellowish fluid that reduces chemicals) and fructose (source of nutrition for sperms).
  • Seminal vesicles: During ejaculation, nutritive and lubricating fluids secreted by seminal vesicles and prostate are added. Fluid secreted by seminal vesicles consists of fructose (energy source for sperms), amino acids, citric acid, phosphorous, potassium, and prostaglandins. Seminal vesicles contribute 50% to semen volume.
  • Prostate: Prostatic secretions comprise about 40% of semen volume and consist of citric acid, acid phosphatase, calcium, sodium, zinc, potassium, proteolytic enzymes, and fibrolysin.
  • Bulbourethral glands of Cowper secrete mucus.
 
Normal values for semen analysis are shown in Tables 835.1 and 835.2.
 
Table 835.1 Normal values of semen analysis (World Health Organization, 1999)
Test Result
1. Volume ≥2 ml
2. pH 7.2 to 8.0
3. Sperm concentration ≥20 million/ml
4. Total sperm count per ejaculate ≥40 million
5. Morphology ≥30% sperms with normal morphology
6. Vitality ≥75% live
7. White blood cells <1 million/ml
8. Motility within 1 hour of ejaculation  
    • Class A ≥25% rapidly progressive
    • Class A and B ≥50% progressive
9. Mixed antiglobuiln reaction (MAR) test <50% motile sperms with adherent particles
10. Immunobead test <50% motile sperms with adherent particles
 
Table 835.2 Biochemical variables of semen analysis (World Helath Organization, 1992)
 1. Total fructose (seminal vesicle marker) ≥13 μmol/ejaculate 
 2. Total zinc (Prostate marker)  ≥2.4 μmol/ejaculate
 3. Total acid phosphatase (Prostate marker)  ≥200U/ejaculate
 4. Total citric acid (Prostate marker)  ≥52 μmol/ejaculate
 5. α-glucosidase (Epididymis marker)  ≥20 mU/ejaculate
 6. Carnitine (Epididymis marker)  0.8-2.9 μmol/ejaculate
 
INDICATIONS FOR SEMEN ANALYSIS
 
Box 835.2 Tests done on seminal fluid
 
• Physical examination: Time to liquefaction, viscosity, volume, pH, color
• Microscopic examination: Sperm count, vitality, motility, morphology, and proportion of white cells
• Immunologic analysis: Antisperm antibodies (SpermMAR test, Immunobead test)
• Bacteriologic analysis: Detection of infection
• Biochemical analysis: Fructose, zinc, acid phosphatase, carnitine.
• Sperm function tests: Postcoital test, cervical mucus penetration test, Hamster egg penetration assay, hypoosmotic swelling of flagella, and computer-assisted semen analysis
Availability of semen for examination allows direct examination of male germ cells that is not possible with female germ cells. Semen analysis requires skill and should preferably be done in a specialized andrology laboratory.
 
  1. Investigation of infertility: Semen analysis is the first step in the investigation of infertility. About 30% cases of infertility are due to problem with males.
  2. To check the effectiveness of vasectomy by confirming absence of sperm.
  3. To support or disprove a denial of paternity on the grounds of sterility.
  4. To examine vaginal secretions or clothing stains for the presence of semen in medicolegal cases.
  5. For selection of donors for artificial insemination.
  6. For selection of assisted reproductive technology, e.g. in vitro fertilization, gamete intrafallopian transfer technique.
 
COLLECTION OF SEMEN FOR INVESTIGATION OF INFERTILITY
 
Semen specimen is collected after about 3 days of sexual abstinence. Longer period of abstinence reduces motility of sperms. If the period of abstinence is shorter than 3 days, sperm count is lower. The sample is obtained by masturbation, collected in a clean, dry, sterile, and leakproof wide-mouthed plastic container, and brought to the laboratory within 1 hour of collection. The entire ejaculate is collected, as the first portion is the most concentrated and contains the highest number of sperms. During transport to the laboratory, the specimen should be kept as close to body temperature as possible (i.e. by carrying it in an inside pocket). Ideally, the specimen should be obtained near the testing site in an adjoining room. Condom collection is not recommended as it contains spermicidal agent. Ejaculation after coitus interruptus leads to the loss of the first portion of the ejaculate that is most concentrated; therefore this method should not be used for collection. Two semen specimens should be examined that are collected 2-3 weeks apart; if results are significantly different additional samples are required.
 
Box 835.3 Semen analysis for initial investigation of infertility
 
• Volume
• pH
• Microscopic examination for (i) percentage of motile spermatozoa, (ii) sperm count, and (iii) sperm morphology
EXAMINATION OF SEMINAL FLUID
 
The tests that can be done on seminal fluid are shown in Box 835.2. Tests commonly done in infertility are shown in Box 835.3. The usual analysis consists of measurement of semen volume, sperm count, sperm motility, and sperm morphology.
 
Terminology in semen analysis is shown in Box 835.4.
 
EXAMINATION OF SEMEN TO CHECK THEEFFECTIVENESS OF VASECTOMY
 
 Box 835.4 Terminology in semen analysis

• Normozoospermia: All semen parameters normal
• Oligozoospermia: Sperm concentration <20 million/ml (mild to moderate: 5-20 million/ml; severe: <5 million/ml)
• Azoospermia: Absence of sperms in seminal fluid
• Aspermia: Absence of ejaculate
• Asthenozoospermia: Reduced sperm motility; <50% of sperms showing class (a) and class (b) type of motility OR <25% sperms showing class (a) type of motility.
• Teratozoospermia: Spermatozoa with reduced proportion of normal morphology (or increased proportion of abnormal forms)
• Leukocytospermia: >1 million white blood cells/ml of semen
• Oligoasthenoteratozoospermia: All sperm variables are abnormal
• Necrozoospermia: All sperms are non-motile or non-viable
The aim of post-vasectomy semen analysis is to detect the presence or absence of spermatozoa. The routine follow-up consists of semen analysis starting 12 weeks (or 15 ejaculations) after surgery. If two successive semen samples are negative for sperms, the semen is considered as free of sperm. A follow-up semen examination at 6 months is advocated by some to rule out spontaneous reconnection.
 
Further Reading:
 
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