stercobilin

Stercobilin is a brownish pigment formed in the intestine from bilirubin, one of the chief breakdown products of heme. It is a major pigment in feces and is largely responsible for the typical brown color of stool.

Formation and metabolism: Bilirubin is processed in the liver where it is conjugated and excreted into bile. In the intestine, gut bacteria deconjugate bilirubin and convert it to urobilinogen. Some urobilinogen is reabsorbed and may be re-excreted in bile or urine as urobilin. The portion that remains in the gut is oxidized to stercobilin (and related bile pigments), which gives feces their characteristic brown color. Stercobilinogen is a related precursor that can be oxidized to stercobilin.

Clinical notes: In healthy individuals, stercobilin is present in stool and gives it its brown color. Obstruction of bile flow or other conditions that reduce bilirubin excretion into the intestine can lead to pale or clay-colored stools due to diminished stercobilin production. Urine color changes may accompany bilirubin metabolism disturbances due to shifts in bilirubin and urobilinogen excretion.

Relation to other pigments: Stercobilin is part of a family of heme-derived pigments that also includes urobilin, which predominates as a pigment in urine. Together, these compounds reflect the gut and liver processing of heme and bilirubin during digestion.