What does the Indirect (Unconjugated) Bilirubin test measure?

Why is Indirect (Unconjugated) Bilirubin measured?

Isolated elevation of indirect bilirubin signals either increased bilirubin production (haemolysis, ineffective erythropoiesis) or impaired hepatic conjugation (Gilbert syndrome, Crigler–Najjar syndrome). The pattern of bilirubin elevation — predominantly indirect versus direct — is the first discriminator in the work-up of jaundice, guiding the clinician toward a prehepatic, hepatic, or posthepatic cause.

Reference ranges

Standard reference

Calculated as total bilirubin minus direct bilirubin; approximately 3–17 µmol/L (0.2–0.9 mg/dL).

Functional medicine optimal

In the absence of haemolysis or inherited disorders, indirect bilirubin should remain within the laboratory reference interval; persistently mildly elevated unconjugated bilirubin in an otherwise healthy individual is typical of Gilbert syndrome.

Units

µmol/L, mg/dL

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.