Bilirubin in Biliary Obstruction

Extrahepatic Obstruction

1. Causes: Stone in the common bile duct; carcinoma in the head of the pancreas

2. Initially causes an increase in conjugated bilirubin

3. Later, unconjugated bilirubin increases, with stabilization of the ratio at about 1:1 conjugated:unconjugated

Intrahepatic Obstruction

1. Causes: Multiple (hepatitis, drug/alcohol injury, active cirrhosis, congestion, metastatic tumor)

2. Variable increase in both conjugated and unconjugated bilirubin, so ratio differs between patients

A relative increase in conjugated bilirubin tends to suggest some type of obstruction; a relative increase in unconjugated bilirubin tends to suggest increased bilirubin production or (less commonly) hepatocellular disease