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)