Bilirubin analysis

Bilirubin is both a precursor and a product of liver metabolism.

Three forms circulate:

1. Unconjugated bilirubin ("indirect")
2. Bilirubin covalently conjugated with glucuronide ("direct," normally about 1/3 of the total)
3. Bili-Alb (delta bilirubin)

Elevated bilirubin occurs when:

1. Production of bilirubin is increased by increased breakdown of heme (increases unconjugated bilirubin)
   • Hemolysis of any cause
   • Resorption of hematomas or pulmonary hemorrhage
   • Ineffective erythropoiesis (rapid heme turnover in the bone marrow)

2. Bilirubin excretion is limited (variable increases in unconjugated/conjugated ratio)
   • Hepatocellular disease
   • Cirrhosis
   • Biliary tract obstruction
   • Congenital disorders of bilirubin excretion
   • Drug-induced inhibition of bilirubin excretion (e.g., phenytoin)
   • Congestive heart failure (decreased hepatic blood flow)