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

Bilirubin, a yellow tetrapyrrole pigment derived from heme catabolism, primarily originates from the degradation of hemoglobin in the body, with minor contributions from other hemo proteins. It is essential for liver function and blood cell metabolism. Elevated bilirubin levels in serum indicate potential liver dysfunction, hemolytic anemia, or bile duct obstruction, often manifesting as jaundice. The pigment exists in two measurable forms: direct bilirubin (DBil), which reflects conjugated bilirubin levels and includes bilirubin covalently bound to albumin (delta-bilirubin); and total bilirubin (TBil), encompassing both conjugated and unconjugated forms. Differential measurement aids in precise diagnosis of hepatic and hematologic conditions. In newborns, elevated bilirubin necessitates prompt management to prevent kernicterus, underscoring the critical role of bilirubin testing in diagnosing and managing liver and blood disorders effectively.

Why is this test performed?

This test is performed for the diagnosis and differentiation of jaundice, as well as in assessing hemolytic anemia in both adults and newborns. It is particularly valuable for evaluating liver function and monitoring treatment progress.

Sample Collection

The test requires the patient's serum, and there are no fasting prerequisites. It can be conducted using a random blood sample from the patient. Typically, 3 to 5 ml of blood is drawn into a plain test tube and allowed to clot to obtain a clear serum. In infants, the sample may be collected via a heel prick.

The blood sample is centrifuged for 5 to 10 minutes to separate the serum, which is then kept stable at 4°C for up to three days. It is crucial to protect the serum from light exposure.

Precautions

• Avoid hemolysis when collecting the sample.
• Protect the sample from light, as exposure can decrease bilirubin levels.
• If testing is delayed, store the sample in a dark, refrigerated environment.
• Handle the test tube gently to prevent inaccurate results.

Pathophysiology

1. Hemoglobin Metabolism: The test measures the end product of hemoglobin metabolism.
2. RBC Breakdown: Hemoglobin from broken down red blood cells (RBCs) is released as heme and globin. Heme is further metabolized to biliverdin, which is then converted into bilirubin.
3. Liver Dysfunction Indicator: Elevated bilirubin levels indicate liver dysfunction.
4. Bile Component: Bilirubin is a component of bile, transported from the liver to the gallbladder, and then to the intestine.
5. Bile Composition: Bile comprises bilirubin, bicarbonate (HCO₃), phospholipids, cholesterol, bile salts, and water.
6. Intestinal Metabolism: Bilirubin is further metabolized in the intestine, where most of it is excreted in the feces.
7. Jaundice Indicator: High bilirubin levels cause the yellowing of the skin and eyes, known as jaundice.
8. Indirect Bilirubin: Unconjugated bilirubin, which binds to albumin, is referred to as indirect bilirubin.
9. Conjugated Bilirubin: In the liver, bilirubin conjugates with glucuronic acid, forming direct or conjugated bilirubin, which no longer binds to protein.
10. Jaundice Threshold: Jaundice becomes apparent when bilirubin levels exceed 2.5 mg/dl.
11. Treatment Threshold: Immediate treatment is required when bilirubin levels exceed 15 mg/dl to prevent brain damage.
12. Physiologic Jaundice: This condition typically appears after 3 to 4 days in newborns and resolves on its own.
13. Kernicterus Risk: In newborns, unconjugated bilirubin can cross the blood-brain barrier if levels rise significantly, potentially causing toxic brain injury known as kernicterus.

Types of jaundice

Jaundice can be categorized into the following types based on the underlying etiology:

1. Pre-hepatic Jaundice: This form of jaundice originates from factors preceding the liver, such as excessive hemolysis of red blood cells (RBCs).
2. Hepatic Jaundice: This type results from liver dysfunction due to hepatic diseases, such as hepatitis.
3. Post-hepatic Jaundice: Also known as obstructive jaundice, this form is caused by conditions occurring after the liver, such as cancer or gallstones.

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

• In newborns, the liver's immaturity and insufficient conjugating enzymes lead to elevated levels of unconjugated bilirubin.
• This unconjugated bilirubin can cross the blood-brain barrier, potentially causing encephalopathy, known as kernicterus.

A bilirubin level exceeding 15 mg/dl in newborns necessitates immediate treatment.

• Treatment options include blood exchange transfusion or phototherapy.

Elevated Bilirubin Levels Are Observed In:

• Liver Damage: Conditions such as cirrhosis, hepatitis, and mononucleosis can lead to increased bilirubin levels.
• Infections: Infections like cholecystitis and infected gallbladders can cause elevated bilirubin.
• Inherited Diseases: Conditions such as Gilbert’s syndrome may result in jaundice; however, Gilbert’s syndrome itself is typically harmless.
• Bile Duct Blockage: Diseases that obstruct the bile ducts, including pancreatic cancer or gallstones, can raise bilirubin levels.
• Medications: Certain medications can increase bilirubin levels. These include various antibiotics, diazepam (Valium), some oral contraceptives, phenytoin (Dilantin), flurazepam (Dalmane), and indomethacin (Indocin).
• Hemolysis: Rapid destruction of red blood cells, which can occur due to allergic reactions to blood transfusions (transfusion reactions) or conditions like sickle cell disease, can lead to elevated bilirubin levels.

Decreased Bilirubin Levels Are Observed In:

• Medications: Certain medications can result in decreased bilirubin levels. These include phenobarbital, vitamin C (ascorbic acid), and theophylline.

Bilirubin Levels Requiring Treatment in Full-Term, Healthy Infants

• Infants 24 Hours or Younger: Treatment is necessary if bilirubin levels exceed 10 mg/dL (170 mmol/L).
• Infants 25 to 48 Hours Old: Treatment is warranted when bilirubin levels exceed 15 mg/dL (255 mmol/L).
• Infants 49 to 72 Hours Old: Treatment is indicated if bilirubin levels surpass 18 mg/dL (305 mmol/L).
• Infants Older than 72 Hours: Treatment should be administered when bilirubin levels are above 20 mg/dL (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