tbili

TBili, or total bilirubin, is a blood test value that represents the sum of direct (conjugated) and indirect (unconjugated) bilirubin in serum. Bilirubin is produced from the breakdown of heme in red blood cells. Unconjugated bilirubin is transported to the liver, where it is conjugated with glucuronic acid and then excreted in bile. TBili thus reflects the overall burden of bilirubin in the body.

Measurement and interpretation: TBili is measured in serum using colorimetric or enzymatic assays. Results are reported in milligrams per deciliter (mg/dL) or micromoles per liter (μmol/L). In adults, a typical normal range is about 0.3 to 1.2 mg/dL (roughly 5 to 21 μmol/L). Elevations in TBili may indicate jaundice and require interpretation alongside direct bilirubin measurements. When direct bilirubin is elevated, it suggests impaired excretion or cholestasis; when indirect bilirubin is elevated, it can indicate increased production or impaired hepatic uptake/conjugation.

Causes and patterns: A predominantly indirect (unconjugated) rise can occur with hemolysis, impaired bilirubin uptake by the liver, or genetic conditions such as Gilbert syndrome. A predominantly direct (conjugated) rise points toward hepatocellular disease (such as hepatitis or cirrhosis) or biliary obstruction (such as gallstones or pancreatic disease). Other factors include certain medications and systemic illnesses.

Special considerations: In newborns, physiologic jaundice commonly elevates TBili and usually resolves without treatment, though very high levels require clinical evaluation. TBili is commonly used as part of liver function testing to help assess liver function, bilirubin metabolism, and biliary drainage in various clinical contexts.