What does the Total Bilirubin, Serum test measure?

Why is Total Bilirubin, Serum measured?

Total bilirubin within the CMP provides the first-line hepatobiliary and haemolytic screen. Elevation above 1.2 mg/dL triggers clinical assessment for jaundice — at approximately 2.5–3.0 mg/dL, scleral icterus becomes clinically apparent. In the pattern context of the full CMP: elevated total bilirubin with elevated ALT and AST suggests hepatocellular injury; elevated total bilirubin with elevated ALP (if reported) suggests cholestatic disease; elevated total bilirubin with normal liver enzymes in a young adult with mild elevation (1.5–3.0 mg/dL) is consistent with benign Gilbert's syndrome (unconjugated hyperbilirubinaemia from UGT1A1 variant — confirmed by normal direct bilirubin on fractionation). Isolated mild total bilirubin elevation in an asymptomatic patient with otherwise normal CMP is most commonly Gilbert's syndrome and requires no further investigation beyond direct bilirubin fractionation for confirmation.

Reference ranges

Standard reference

0.1–1.2 mg/dL (1.71–20.52 µmol/L) # REVIEWER FLAG: Confirm Quest Diagnostics reference range for total bilirubin. The upper limit varies between 1.0 and 1.2 mg/dL depending on the platform.

Functional medicine optimal

0.3–0.8 mg/dL (functional medicine optimal; emerging research suggests mildly elevated bilirubin within the reference range may have antioxidant and cardioprotective effects — framing as a harmful outlier is not warranted at 1.0–1.2 mg/dL). # REVIEWER FLAG: The antioxidant-cardioprotective framing of modestly elevated bilirubin is an area of active research — reviewer to confirm whether this warrants mention or removal.

Units

mg/dL, µmol/L

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