Bilirubin is produced in the liver when it breaks down old red blood cells, states WebMD. It then circulates through the bloodstream as conjugated, or direct, or unconjugated, or indirect, bilirubin. Total bilirubin levels are measured in the blood, while unconjugated bilirubin levels are derived from total and conjugated bilirubin levels.
Conjugated bilirubin is made in the liver from unconjugated bilirubin and is water soluble, reports WebMD. Large amounts of bilirubin lead to jaundice, a yellowing around the eyes or of the skin.
Bilirubin levels are tested with a blood or urine sample, and before undergoing a bilirubin level test, patients should not drink or eat for at least four hours. Normal levels of conjugated bilirubin are zero to 0.3 milligrams per deciliter, and normal levels of total bilirubin are 0.3 to 1.9 milligrams per deciliter, according to MedlinePlus.
Bilirubin tests are conducted to check for gallstones, pancreatic tumors, a biliary stricture or other conditions that result from blocked bile ducts, reports WebMD. Abnormal bilirubin levels may also indicate liver malfunction or liver disease, such as cirrhosis, hepatitis or damage from medication. Bilirubin tests may also indicate hemolytic anemia, which causes increased destruction of red blood cells.
Bilirubin tests on newborns help determine whether newborns with neonatal jaundice need phototherapy or a blood transfusion, states MedlinePlus. Most newborns have some jaundice.