Bilirubin, a brownish yellow substance, is produced by the body when it breaks down spent red blood cells. After processing in the liver, the material is then expelled by the bowels. The two kinds of bilirubin are indirect and direct.
Indirect bilirubin is found in the blood stream and is also called unconjugated bilirubin. It takes the old red blood cells to the liver for processing. At this point the bilirubin does not dissolve in water.
Direct, or conjugated, bilirubin is the substance created by the liver. The bilirubin is changed from the insoluble form to a soluble substance that can be absorbed and disposed of by the bowel. Since red blood cells are being replaced constantly, both types of bilirubin are needed, in the correct proportions, for healthy bodies.
If patients display signs of jaundice, such as a yellow tint to the skin or eyes, they may have too much bilirubin and a blood test is warranted. This test checks for problems such as jaundice, hepatitis, anemia, bile duct blockage and general liver function.
Adults needing a bilirubin test must fast for four hours prior to blood being drawn. There is no preparation for children. The test measures both indirect and direct bilirubin levels, as well as combined totals. Patients that have levels higher or lower than normal may need further tests.