A bilirubin test measures the levels of bilirubin in your blood. Bilirubin (bil-ih-ROO-bin) is a yellowish pigment that is made during the breakdown of red blood cells. Bilirubin passes through the liver and is eventually excreted out of the body.

Higher than usual levels of bilirubin may indicate different types of liver or bile duct problems. Sometimes, higher bilirubin levels may be caused by an increased rate of destruction of red blood cells.

Bilirubin testing is usually one of a group of tests to check the health of your liver. Bilirubin testing may be done to:

• Investigate jaundice — a yellowing of the skin and eyes caused by high levels of bilirubin. This test is commonly used to measure bilirubin levels in newborns with infant jaundice.
• Determine whether there might be blockage in your bile ducts, in either the liver or the gallbladder.
• Help detect liver disease, particularly hepatitis, or monitor its progression.
• Help evaluate anemia caused by the destruction of red blood cells.
• Help follow how a treatment is working.
• Help evaluate a suspected drug toxicity.

Some common tests that might be done at the same time as bilirubin testing include:

• Liver function tests. Blood tests that measure certain enzymes or proteins in your blood.
• Albumin and total protein. Levels of albumin — a protein made by the liver — and total protein show how well your liver is making certain proteins. These proteins are necessary for your body to fight infections and perform other functions.
• Complete blood count. This test measures several components and features of your blood.
• Prothrombin time. This test measures the clotting time of plasma.

Bilirubin testing is done using a blood sample. Usually, the blood is drawn through a small needle inserted into a vein in the bend of your arm. A small tube is attached to the needle to collect the blood.

You may feel a quick pain as the needle is inserted into your arm. You also may experience some short-term discomfort at the site after the needle is removed. Blood for bilirubin testing in newborns is usually collected using a sharp lancet to break the skin of the heel. This is known as a heel stick. There may be slight bruising at the puncture site afterward.

Your blood will be sent to a laboratory for analysis. You can usually return to normal activities immediately.

Bilirubin test results are expressed as direct, indirect or total bilirubin. Total bilirubin is a combination of direct and indirect bilirubin. Typically, you'll get results for direct and total bilirubin.

Typical results for a total bilirubin test are 1.2 milligrams per deciliter (mg/dL) for adults and usually 1 mg/dL for those under 18. Typical results for direct bilirubin are generally 0.3 mg/dL.

These results may vary slightly from laboratory to laboratory. Results may be slightly different for women and children. Results also may be affected by certain foods, medicines or demanding exercise. For this reason, be sure to tell your health care provider about your activity levels, as well as any foods or medicines you've taken.

Lower than usual bilirubin levels are usually not a concern. Higher levels of direct bilirubin in your blood may indicate your liver isn't clearing bilirubin properly. This may indicate liver damage or disease. Higher levels of indirect bilirubin may be a sign of other problems.

One common, and harmless, cause of elevated bilirubin is Gilbert's syndrome, a deficiency in an enzyme that helps break down bilirubin. Your health care provider may order more tests to investigate your condition. Bilirubin test results also may be used to monitor certain conditions, such as jaundice.