Bilirubinuria (Urinary Bilirubin)

• Bile (mainly conjugated bilirubin) is converted to urobilinogen by intestinal bacteria. Most of the urobilinogen is excreted in faeces or reabsorbed and transported back to the liver to be converted back into bile. The remaining urobilinogen (about 1% of total) is excreted in the urine.
• The amount of conjugated bilirubin present in serum in healthy subjects is small (less than 10% of total bilirubin). An elevated level of conjugated serum bilirubin implies liver disease. Therefore, because only conjugated bilirubin appears in urine, bilirubinuria also implies liver disease.
• Unconjugated bilirubin is tightly bound to albumin, not filtered by the glomerulus and absent from urine even with raised serum levels of unconjugated bilirubin. A positive test for urine bilirubin confirms that any raised plasma levels are from conjugated hyperbilirubinaemia.
• In the assessment of a patient with raised total bilirubin, urinanalysis for bilirubin and urobilinogen, together with liver function tests may be helpful in identifying the underlying pathology.

• Unconjugated
  • Albumin-bound in serum
  • Measured as indirect-reacting bilirubin
  • Never present in urine
• Conjugated
  • Unbound in serum
  • Measured as direct-reacting bilirubin
  • Present in urine

• The bilirubin pad on the multireagent dipstick detects bilirubin using a specific diazo reagent. It allows a very approximate quantification of bilirubinuria.
• The colour change indicating a positive reaction may be a subtle transition among shades of beige and is sometimes is obscured by colour of the urine itself (e.g. in marked haemoglobinuria).

Raised conjugated bilirubin (bilirubinuria)

• Hepatocellular disease and post-hepatic or cholestatic disease (intrahepatic and extrahepatic), including drug toxicity as well as pancreatic causes of obstructive jaundice. An early feature of hepatobiliary disease can be bilirubinuria, which develops in acute viral hepatitis even before clinical jaundice appears. It may be absent, however, under other circumstances despite increased serum bilirubin.
• Inherited defects in excretion, e.g. Dubin-Johnson syndrome, Rotor syndrome.

Raised unconjugated bilirubin (no bilirubinuria)

• Gilbert's syndrome (4% of the population)
• Haemolysis
• Post viral hepatitis
• Mild chronic hepatitis
• Crigler-Najjar syndrome

Urinary urobilinogen

• Normally excreted in small amounts into the urine.
• Very sensitive but non-specific test to determine liver damage, haemolytic disease and severe infections.
• Increases in early hepatitis, mild liver cell damage and mild toxic injury, even without an increase in serum bilirubin.
• Decreased or absent in obstructive jaundice.

• False negative:
  • Aged urine samples: Conjugated bilirubin hydrolyzes to unconjugated bilirubin if left at room temperature.
  • Exposure to UV light: UV light converts bilirubin to biliverdin, resulting in false negative reactions.
  • Patient taking rifampicin.
  • Ascorbic acid: High concentrations of vitamin C inhibit the reaction.
• False positive:
  • Patient taking phenothiazines.