Merck, B4126-5G, Bilirubin

Bilirubin, an end product of heme catabolism, forms from the breakdown of erythrocyte hemoglobin in the reticuloendothelial system. Heme oxygenase converts the heme of hemoglobin to biliverdin, and subsequently an NADPH-dependent biliverdin reductase converts biliverdin to bilirubin. Bilirubin is commonly found bound to serum albumin, when circulating in blood, in its dianion form. Bilirubin is also associated with bile salts, in its monoanion form. Disorders of hyperbilirubinemia may occur due to increased bilirubin synthesis or decreased bilirubin clearance.