Clinical laboratory professional specialized to external quality assessment (proficiency testing) schemes for Laboratory medicine and clinical pathology. Author/Writer/Blogger
The microscope is the most important piece of equipment in the clinic laboratory. The microscope is used to review fecal, urine, blood, and cytology samples on a daily basis (see Figure). Understanding how the microscope functions, how it operates, and how to care for it will improve the reliability of your results and prolong the life of this valuable piece of equipment.
Used to carry the microscope.
Supports the microscope and houses the light source.
The lens of the microscope you look through. The ocular also magnifies the image. The total magnification can be calculated by multiplying the objective power by the ocular power. Oculars come in different magnifications, but 10× magnification is common.
The purpose of the diopter adjustment is to correct the differences in vision an individual may have between their left and right eyes.
This allows the oculars to move closer or further away from one another to match the width of an individual’s eyes. When looking through the microscope, one should see only a single field of view. When viewing a sample, always use both eyes. Using one eye can cause eye strain over a period of time.
The nosepiece holds the objective lenses. The objectives are mounted on a rotating turret so they can be moved into place as needed. Most nosepieces can hold up to five objectives.
The objective lens is the lens closest to the object being viewed, and its function is to magnify it. Objective lenses are available in many powers, but 4×, 10×, 40×, and 100× are standard. 4× objective is used mainly for scanning. 10× objective is considered “low power,” 40× is “high power” and 100× objective is referred to as “oil immersion.” Once magnified by the objective lens, the image is viewed through the oculars, which magnify it further. Total magnification can be calculated by multiplying the objective power by the ocular lens power.
For example: 100× objective lens with 10× oculars = 1000× total magnification.
The platform on which the slide or object is placed for viewing.
Spring-loaded brackets, or clips, hold the slide or specimen in place on the stage.
Located just below the stage are the stage control knobs. These knobs move the slide or specimen either horizontally (x-axis) or vertically (y-axis) when it is being viewed.
The condenser is located under the stage. As light travels from the illuminator, it passes through the condenser, where it is focused and directed at the specimen.
Allows the condenser to be raised or lowered.
These crews center the condenser, and therefore the beam of light. Generally, they do not need much adjustment unless the microscope is moved or transported frequently.
This structure controls the amount of light that reaches the specimen. Opening and closing the iris diaphragm adjusts the diameter of the light beam.
These knobs bring the object into focus by raising and lowering the stage. Care should be taken when adjusting the stage height. When a higher power objective is in place (100× objective for example), there is a risk of raising the stage and slide and hitting the objective lens. This can break the slide and scratch the lens surface. Coarse adjustment is used for finding focus under low power and adjusting the stage height. Fine adjustment is used for more delicate, high power adjustment that would require fine tuning.
The illuminator is the light source for the microscope, usually situated in the base. The brightness of the light from the illuminator can be adjusted to suit your preference and the object you are viewing.
Kohler illumination is a method of adjusting a microscope in order to provide optimal illumination by focusing the light on the specimen. When a microscope is in Kohler, specimens will appear clearer, and in more detail.
It is necessary to follow a standard procedure for specimen collection to get the most accurate and trustworthy results of the laboratory test. The blood sample can be collected from the venipuncture or skin puncture for the hematological investigations.
This method is most common and mostly used in infants and small children and if the small amount of blood is required. This method is suitable for the estimation of hemoglobin, cell counts, determination of hematocrit (HCT) or packed cell volume (PCV) by micro method and preparation of blood films. Blood obtained by this method is also called as capillary blood. However, it is the mixture of blood from arterioles, venules, and capillaries. It also contains small amount of tissue fluid. In infants, blood is collected from the heel (the medial or lateral aspect of plantar surface or great toe). In adults, it is collected from the side of a middle or ring finger (distal digit) or from the earlobe. (see Figure 796.1).
The puncture site is cleansed with the 70% ethanol or another suitable disinfectant. After drying, a puncture is made with a sterile, dry, disposable lancet, in deep to allow free flow of blood. The first drop of blood is wiped away with the dry and sterile cotton as it contains tissue fluid. After wiping the first drop of blood, next few drops of blood are collected. Excessive pressing should be avoided, as it may dilute the blood with the tissue fluid. After collection of blood, a piece of dry and sterile cotton is pressed over the puncture site till the bleeding ends. Hemoglobin, red cell count and hematocrit (HCT) or packed cell volume (PCV) are moderately higher in the blood collected from skin puncture, as compared to the venous blood. The reason behind this scenario is that platelets adhere to the puncture site and cause the lower count of platelet, and due to small sample size, instant repeat testing is not possible if the result is abnormal or unusual.
Avoid collecting blood from cold, cyanosed skin since the false elevation of values of red blood cells, white blood cells and hemoglobin will be obtained.
Venous blood is obtained when the larger quantity of blood is needed to perform multiple tests. Different test tubes are filled with blood as per requirement of anticoagulant and blood ratio for the test. Anticoagulant is not required for the test performed by the serum.
|Dipotassium EDTA||20 gm|
|Distilled water||200 ml|
|Ammonium oxalate||1.2 gm|
|Potassium oxalate||0.8 gm|
|Distilled water||upto 100 ml|
|Trisodium citrate||3.2 gm|
|Distilled water||upto 100 ml|
Use 1:9 (anticoagulant: blood) proportion for coagulation studies; for ESR, 1:4 proportion is recommended.
There are two methods for ABO grouping:
Both cell and serum grouping should be done since each test acts as a check on the other.