Urobilinogen in Urine Analysis

Urobilinogen in Urine

• Conjugated bilirubin, complexed with cholesterol, bile salts, and phospholipids, travels to the duodenum via bile.
• Bacteria in the colon hydrolyze the conjugated bilirubin, reducing it to urobilinogen, mesobilirubinogen and stercobilinogen.
• Up to 50% of urobilinogen is reabsorbed into the portal circulation, then re-excreted into bile, in an unconjugated form.
• Most of the remaining urobilinogen is excreted via the feces as colored urobilins or stercobilin (after further hydrogen removal).
• A small amount of urobilinogen is excreted in urine.
• Urobilinogen is measured in "units" (roughly equivalent to milligrams per deciliter), as it represents a mixture of compounds.

Normal Levels

• Normal urine urobilinogen output is 0.5–2.5 mg or units per 24 hours.
• Urobilinogen is colorless and unstable (labile), contrasting with urobilins (its oxidized form), which give urine its yellow-orange hue.

Factors Influencing Urobilinogen Excretion

• Alkaline urine increases urobilinogen excretion.
• Acidic urine decreases urobilinogen excretion.
• Elevated levels in the urine indicate liver issues, such as impaired removal from the portal circulation.

Liver Dysfunction and Urobilinogen

• Hepatocellular damage (viral hepatitis, drugs, toxins, or cirrhosis) can result in increased urobilinogen excretion as the liver struggles to remove it.
• Liver congestion (e.g., from congestive heart failure) prevents efficient urobilinogen re-excretion into bile, leading to higher urine levels.