Bilirubin: Total, Direct and Indirect Bilirubin (Different Types of Jaundice)

Why is this test performed?

This test is performed for the diagnosis and differentiation of jaundice. This test is also done in a patient with hemolytic anemia in adult and newborn. This test is very useful to evaluate liver functions and for the follow-up of a patient with treatment.

Collection of sample

This test is performed with the patient's serum. There is no restriction for a fasting sample. The test can be done by a random blood sample the patient.

About 3 to 5 ml of blood is collected in a plain test tube, and blood is allowed to clot to get clear serum. In infants, the sample may be collected from the heel.

The blood sample is centrifuged for 5 to 10 minutes and the serum is separated for the test. The patient's serum is stable at 4° C for 3 days and protects it from the light.

Precautions

• Avoid sample from hemolysis
• Do not expose the sample to light. Exposure of sample to light may decrease the value.
• If there is a delay in performing the test then keep the sample in dark and refrigerate it.
• Avoid shaking of the test tube as it may lead to an inaccurate result.

Pathophysiology

1. This is the end product of hemoglobin metabolism.
2. From the breakdown of RBC, hemoglobin is released in form of Heme and Globin. Heme is further metabolized to Biliverdin and this is transformed into bilirubin.
3. The raised level of bilirubin is the indicator of liver dysfunction.
4. Bilirubin is a component of bile which is transported from the liver and stored in the gallbladder and from that organ, it is it is delivered to the intestine.
5. Bile formed in the liver. It is made up of bilirubin, bicarbonate (HCO₃), phospholipids, cholesterol, bile salts, and water.
6. Further metabolism of bilirubin takes place in the intestine.
7. Most of it is metabolized in the intestine and discharged in the feces.
8. An increased level of bilirubin causes the yellow color of the skin and jaundice (conjunctiva).
9. The bilirubin which is not conjugated to the liver, attach to albumin (carrying protein) is called Indirect bilirubin.
10. The bilirubin conjugate with the glucuronic acid. This process takes place in the liver and gives rise to direct or conjugated bilirubin. Now conjugated bilirubin is no more bound to protein.
11. Jaundice occurs when the bilirubin level is above 2.5 mg/dl.
12. When the bilirubin level exceeds 15 mg/dl then the treatment is immediately started to avoid the brain damage.
13. While physiologic jaundice appears after 3 to 4 days and subsidies itself.
14. In the newborn, when the liver can not conjugate bilirubin and if the level increases then this indirect bilirubin can cross the blood-brain barrier which may lead to toxic injury to the brain and called Kernicterus.

Types of jaundice

Types of jaundice are defined as follows:

• Pre-hepatic jaundice: The etiology is before the liver like excessive hemolysis of RBC.
• Hepatic jaundice: Dysfunction of the liver caused by hepatic diseases e.g. hepatitis.
• Post-hepatic jaundice: The cause is after the liver like cancer, gallstone, etc. These are the obstructive type of jaundice.

Calculation of total, direct and indirect bilirubin

Total bilirubin is calculated as follows:

Total bilirubin = Direct bilirubin + Indirect bilirubin

Direct bilirubin is calculated as follows:

Direct bilirubin = Total bilirubin – Indirect bilirubin

Indirect bilirubin is calculated as follows:

Indirect bilirubin = Total bilirubin – Direct bilirubin

Normal Values

• Total bilirubin 0.3 to 1.0 mg/dL or 5.1 to 17.0 mmol/L
• Direct bilirubin 0.1 to 0.3 mg/dL or 1.0 to 5.1 mmol/L
• Indirect bilirubin 0.2 to 0.7 mg/dL or 3.4 to 11.9 mmol/L

Total bilirubin in

• Umbilical cord blood less than 2 mg/ dl

Normal values of total bilirubin in infants

• 0 to 1 days less than 6 mg/ dl
• 0 to 2 days less than 8 mg/ dl
• 3 to 5 days less than 12 mg/dl
• after 5 days less than 0.2 to 1.0 mg/ dl

Physiologic jaundice of the newborn

• This is found in the newborn when the liver is immature and an insufficient amount of conjugating enzymes. This will lead to an increased amount of unconjugated bilirubin.
• This unconjugated bilirubin can cross the blood-brain barrier and give rise to encephalopathy (Kernicterus).

Bilirubin level more than 15 mg/dl in newborn needs immediate treatment.

• This is treated by the exchange of blood or light therapy.

Raised Bilirubin level is seen in

• Diseases that cause liver damage, such as cirrhosis, hepatitis, or mononucleosis.
• In some infections, such as cholecystitis, and an infected gallbladder.
• In some inherited diseases, such as Gilbert’s syndrome. Although jaundice may occur in some people with Gilbert’s syndrome, the condition is not harmful.
• In some diseases that cause blockage of the bile ducts, such as cancer of the pancreas or gallstones.
• Medicines that may increase the level of bilirubin. This consist of many antibiotics, diazepam (Valium), some types of birth control pills, phenytoin (Dilantin), flurazepam (Dalmane), and indomethacin (Indocin).
• Rapid destruction of red blood cells in the blood, such as from an allergic reaction to blood received during a transfusion (called a transfusion reaction) or sickle cell disease.

Decreased Bilirubin level is seen in

• Medicines that may decrease the level of bilirubin. This includes phenobarbital, vitamin C (ascorbic acid), and theophylline.

Bilirubin levels that may require treatment in a full-term, healthy baby

• 24 hours or younger infant needs to be treated if the level of bilirubin is more than 10 mg/dL or more than 170 mmol/L.
• 25 to 48 hours infant needs to be treated when the level of bilirubin is more than 15 mg/dL or more than 255 mmol/L.
• 49 to 72 hours infant needs to be treated when bilirubin level is more than 18 mg/dL or more than 305 mmol/L
• Older than 72 hours infant need to be treated when the bilirubin level is more than 20 mg/dL or more than 340 mmol/L

Causes of direct hyperbilirubinemia

If the direct bilirubin level is more than 50%.

1. Gallbladder tumors
2. Gallstones
3. Dubin-Johnson syndrome
4. Rotor syndrome
5. Obstruction of extrahepatic ducts or inflammatory scarring
6. Can be resolved by the surgery
7. Drugs may cause cholestasis

Causes of Indirect hyperbilirubinemia

If the indirect bilirubin level is less than 15 to 20%.

1. Hepatitis
2. Increased RBC hemolysis ( Erythroblastosis fetalis)
3. Sickle cell anemia
4. Congenital enzyme deficiency
5. Cirrhosis
6. Gilbert syndrome
7. Crigler-Najjar syndrome
8. Drugs
9. Transfusion reactions
10. There is no role of surgery