Urobilinogen in Urine Analysis

Study Notes

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.

Description

This quiz explores the formation, measurement, and normal levels of urobilinogen in urine. It covers the biochemical processes involving bilirubin and the factors influencing urobilinogen excretion. Test your understanding of this important metabolic compound and its significance in urine analysis.