Bilirubin metabolism

Bilirubin, a degradation product of heme, is produced largely by metabolism of hemoglobin released from senescent red blood cells. Other sources of bilirubin include turnover of heme-containing proteins such as cytochromes, hemolytic disorders, and ineffective erythropoiesis as seen in thalassemias. Bilirubin has been an object of study for many years, but it is probably its yellow color rather than its physiologic importance that has driven these investigations. Under rare circumstances, especially in premature babies with hyperbilirubinemia, bilirubin can cross the blood-brain barrier and cause kernicterus, a neurologic syndrome that may result in severe developmental deficits and death. Recent studies suggest that in normal adults bilirubin may have some role as an antioxidant. This chapter reviews the subjects of bilirubin metabolism and transport.