urobilinogen

Urobilinogen is a colorless, water-soluble product of bilirubin metabolism that forms in the intestine. After bilirubin is conjugated in the liver and secreted into bile as bilirubin diglucuronide, intestinal bacteria reduce and hydrolyze it to urobilinogen. This compound can follow several fates: a portion is reabsorbed from the gut into the portal circulation and returned to the liver (enterohepatic circulation), a portion is excreted by the kidneys into urine, and some is further oxidized by gut bacteria to colored products such as urobilin and stercobilin, contributing to stool color.

Normal levels and testing can vary by laboratory, but urobilinogen is typically present in urine at low concentrations. Urine urobilinogen is often measured as part of urinalysis using colorimetric methods; values commonly range from about 0.1 to 1 mg/dL in healthy individuals. Its measurement can aid in evaluating hepatic function and biliary tract status, though it is not a standalone diagnostic test.

Clinical significance: increased urinary urobilinogen can occur with conditions that raise bilirubin turnover or hepatic processing, such as hemolytic anemia or acute and chronic liver diseases. Decreased or absent urinary urobilinogen may occur with biliary obstruction or when gut bacteria are reduced (for example, by antibiotics), limiting the formation of urobilinogen in the intestine. Interpreting levels typically requires correlation with bilirubin measurements and clinical context.