Direct Bilirubin

Overview

Direct bilirubin measures the conjugated fraction of bilirubin in serum, representing the portion processed by the liver and water-soluble for biliary excretion. It reflects hepatic conjugation efficiency and biliary patency. Elevated levels indicate cholestasis, hepatocellular dysfunction, Dubin-Johnson syndrome, or Rotor syndrome, while low levels lack clinical significance. Clinically, direct bilirubin distinguishes obstructive from hemolytic or unconjugated hyperbilirubinemia patterns in jaundice evaluation.

Clinical Use Cases

  • Differentiating intrahepatic cholestasis from hepatocellular jaundice.
  • Diagnosing biliary obstruction (choledocholithiasis, pancreatic cancer, strictures).
  • Evaluating conjugated hyperbilirubinemia syndromes (Dubin-Johnson, Rotor).
  • Monitoring neonatal cholestasis and liver transplant function.

Specimen Types

  • Serum (preferred).
  • Plasma (lithium heparin).
  • Whole blood (point-of-care devices).

Measurement Methods

  • Jendrassik-Grof diazo method (direct reaction).
  • Enzymatic-spectrophotometric assays.
  • Dry-slide technology (reflectance spectrophotometry).

Test Preparation and Influencing Factors

  • No fasting required.
  • Hemolysis, lipemia, or hypertriglyceridemia interfere with spectrophotometric methods.
  • Drugs (rifampin, phenobarbital) may alter conjugation or excretion.
  • Neonates have immature conjugation; reference ranges vary by age.

Synonyms

  • Conjugated bilirubin.
  • Direct-reacting bilirubin.
  • DBIL.

Further Reading