bilirubin /bil′iro̅o̅″bin/ [L, bilis + ruber, red] , the orange-yellow pigment of bile, formed principally by the breakdown of hemoglobin in red blood cells after termination of their normal lifespan. Water-insoluble unconjugated bilirubin normally travels in the bloodstream to the liver, where it is converted to a water-soluble, conjugated form and excreted into the bile. In a healthy person, about 250 mg of bilirubin is produced daily. The majority of bilirubin is excreted in the stool. The characteristic yellow pallor of jaundice is caused by the accumulation of bilirubin in the blood and in the tissues of the skin. Testing for bilirubin in the blood provides information for diagnosis and evaluation of liver disease, biliary obstruction, and hemolytic anemia. Normal levels of total bilirubin are 0.1 to 1.2 mg/dL or 2 to 21 μmol/L. See also jaundice.
