What is a bilirubin test?

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 of bilirubin does not 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) and is made by the liver from indirect bilirubin.

Total bilirubin and direct bilirubin levels are measured directly in the blood, whereas 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 appear 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 does not 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.

A bilirubin test measures the level of bilirubin circulating in the blood. Bilirubin is a by-product of the normal process of breakdown of red-blood cells. Normally the bilirubin is carried by the blood to the liver where it is removed. However some conditions interfere with this normal process and leads to elevated levels of bilirubin level in the blood. A bilirubin test gives three numerical results, total bilirubin, indirect bilirubin and direct bilirubin.

Indirect or unconjugated bilirubin which is the measure of bilirubin in the blood before it reaches the liver. In an unconjugated form bilirubin is insoluble and the body is unable to excrete it. Direct or conjugated bilirubin is the amount of bilirubin present, after it has passed through the liver and changed to a soluble for that will be excreted in the feces.