Test Overview

A bilirubin test measures the amount of bilirubin in a blood sample. Bilirubin is a brownish yellow substance found in bile. It is produced when the liver breaks down old red blood cells. Bilirubin is then removed from the body through the stool (feces) and gives stool its normal color.

Bilirubin circulates in the bloodstream in two forms:

Indirect (or unconjugated) bilirubin.

This form doesn't dissolve in water. (It is insoluble.) Indirect bilirubin travels through the bloodstream to the liver, where it is changed into a soluble form (direct or conjugated).

Direct (or conjugated) bilirubin.

Direct bilirubin dissolves in water. (It is soluble.) It's made by the liver from indirect bilirubin.

Total bilirubin and direct bilirubin levels are measured directly in the blood. Indirect bilirubin levels are derived from the total and direct bilirubin measurements.

When bilirubin levels are high, the skin and whites of the eyes may look yellow (jaundice). Jaundice may be caused by liver disease (hepatitis), blood disorders (hemolytic anemia), or blockage of the tubes (bile ducts) that allow bile to pass from the liver to the small intestine.

Mild jaundice in newborns usually doesn't cause problems. But too much bilirubin (hyperbilirubinemia) in a newborn baby can cause brain damage (kernicterus) and other serious problems. So some babies who develop jaundice may need treatment to lower their bilirubin levels.