Stercobilina

Stercobilina, known in English as stercobilin, is a brown bile pigment that gives feces their characteristic color. It is a product of heme metabolism and represents the final oxidation product derived from bilirubin processing in the intestine.

Biochemical origin and pathway. Heme from aged red blood cells is broken down to biliverdin and then bilirubin. Bilirubin is conjugated in the liver and excreted into bile, which enters the intestine. In the gut, intestinal bacteria modify conjugated bilirubin to form urobilinogen. Some urobilinogen is reabsorbed and returned to the liver or excreted in urine as urobilin; the remainder is oxidized in the intestine to stercobilin, which is excreted in feces. Stercobilin is the major pigment responsible for the brown coloration of stool.

Clinical and diagnostic relevance. The presence of stercobilin in feces reflects normal bile flow and intestinal bacterial processing of bilirubin. Reduced stercobilin formation or excretion, as seen with biliary obstruction or significant liver dysfunction, can lead to paler or clay-colored stools. Conversely, normal production of stercobilin corresponds with typical brown stool coloration. Stercobilin is typically studied in the broader context of bile pigment metabolism, alongside bilirubin and urobilinogen, to assess hepatic and biliary health.