Bilirubin Metabolism: Flow and Clinical Correlates
| Stage | Process | Clinical Implication |
|---|---|---|
| 1. Production | Heme catabolism by the Reticuloendothelial system. | Hemolysis increases production, leading to pre-hepatic jaundice. |
| 2. Transport | Unconjugated bilirubin is bound to albumin. | Displaced by drugs (e.g., sulfonamides), causing kernicterus. |
| 3. Uptake/Conjugation | Liver uptake and glucuronidation (via UGT enzyme). | Deficiency (e.g., Gilbert, Crigler-Najjar) causes unconjugated hyperbilirubinemia. |
| 4. Excretion | Biliary secretion into the intestines. | Obstruction causes conjugated hyperbilirubinemia and pale stools. |
High-Yield Differential Diagnosis:
- Unconjugated Hyperbilirubinemia: Hemolysis, Gilbert syndrome, Crigler-Najjar.
- Conjugated Hyperbilirubinemia: Dubin-Johnson, Rotor syndrome, bile duct obstruction (e.g., gallstones, pancreatic cancer).