Bilirubin

Alternate Names
direct bilirubin
indirect bilirubin
conjugated bilirubin
total bilirubin
unconjugated bilirubin

Definition of Bilirubin

A bilirubin test measures the amount of bilirubin in the blood. Hemoglobin is the protein that binds oxygen in red blood cells. When hemoglobin breaks down, it produces bilirubin which is, in turn, processed by the liver and passed out of the body in the stool. If liver cells are damaged, unprocessed bilirubin can build up in the bloodstream. The indirect (also known as unconjugated) bilirubin test measures the unprocessed bilirubin. . Once bilirubin has been processed in the liver, it can be measured as direct (also known as conjugated) bilirubin. The test known as total bilirubin measures both kinds combined.

Who is a candidate for the test?

The bilirubin test is often done when a healthcare professional suspects liver or gallbladder disease. The person may have jaundice, which causes yellowed eyes and skin. A buildup of bilirubin causes jaundice.

How is the test performed?

To measure bilirubin levels, a lab technician takes a blood sample from a vein in the forearm or hand. First, he or she cleans the skin over the vein with an antiseptic. Next, a rubber tube called a tourniquet is wrapped around the upper arm. This restricts blood flow in the veins in the lower arm, causing them to enlarge.

A fine needle is gently inserted into the enlarged vein, and the tourniquet is removed. Blood flows from the vein through the needle into a vial. After the needle is withdrawn, the technician covers the puncture site with a bandage.

What is involved in preparation for the test?

Generally, nothing is required to prepare for a bilirubin test.

What do the test results mean?

Normal values for total bilirubin are between 0.3 and 1.2 mg/100 ml. Normal conjugated or direct bilirubin levels should be between 0.0 and 0.2 mg/100 ml. The level of unconjugated bilirubin can be calculated by simply subtracting the direct bilirubin value from the total.

Abnormally high unconjugated bilirubin levels can be found in many disorders, including:

• hemolytic anemias, conditions in which too many red cells at a time are breaking down
• cirrhosis, or scarring of the liver
• congenital, or hereditary, problems with the liver
• hepatitis and other liver diseases
• immature liver development in newborns

Abnormally high conjugated bilirubin levels usually indicate that for some reason, bile flow out of the liver has been obstructed. This could be from a gallstone lodged in the bile duct, from a tumor, or a complication from surgery. In this case, the bilirubin has been processed but is backing up into the blood because it cannot be excreted properly.