Viral Hepatitis and Liver Disease Website Course

Evaluating Liver Test Abnormalities

Understanding the Pathophysiology of Liver Disease

for Health Care Providers

Bilirubin Metabolism

  1. Heme, the substrate of bilirubin, is derived from red blood cells that have died.
  2. Heme is degraded to biliverdin by heme oxygenase in the mononuclear phagocytes.
  3. Biliverdin is subsequently reduced to bilirubin by biliverdin reductase.
  4. Circulating bilirubin (insoluble) is bound to albumin and subsequently taken up by the hepatocytes.
  5. To make it soluble, bilirubin undergoes conjugation, a reaction catalyzed by bilirubin UDPglucuronyl transferase (UDPG).
  6. Conjugated bilirubin (soluble) is excreted into bile and reaches the bowel.
  7. Bilirubin glucuronides are deconjugated by colonic bacteria and eliminated in the feces.