Bilirubin

Bilirubin (formerly referred to as hematoidin) is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases. It is responsible for the yellow color of bruises, the yellow color of urine (via its reduced breakdown product, urobilin), the brown color of feces (via its conversion to stercobilin), and the yellow discoloration in jaundice.