stercobilinogen

Stercobilinogen is a colorless bile pigment that arises in the intestinal tract during the breakdown of heme. It is an intermediate in the transformation of bilirubin-derived compounds and acts as a precursor to stercobilin, the brown pigment that gives feces its characteristic color.

In the biosynthetic pathway, heme from aged red blood cells is degraded to biliverdin and then to bilirubin. Bilirubin is transported to the liver, where it is conjugated and excreted into bile. In the intestine, bacterial enzymes reduce conjugated bilirubin to urobilinogen. A portion of urobilinogen is subsequently oxidized to stercobilinogen, which is then converted to stercobilin. Stercobilin is the pigment that imparts brown coloration to feces, while stercobilinogen itself is colorless and rapidly transformed.

Clinical and physiological relevance centers on its role in fecal coloration and its dependence on bile flow and gut microbiota. Normal enterohepatic circulation and intact intestinal bacteria are required for stercobilinogen formation and subsequent stercobilin production; disruptions in bile delivery (such as cholestasis or biliary obstruction) or altered gut flora can reduce stercobilinogen and stercobilin formation, contributing to pale or clay-colored stools. In contrast, urine stercobilinogen and urobilinogen levels can reflect hepatic function and hemolysis, though stercobilinogen is not routinely measured in clinical practice.

See also: urobilinogen, urobilin, stercobilin.