Urine Bilirubin: Multistix

The bilirubin pad on the multireagent dipstick detects bilirubin using a specific diazotization reaction and is sensitive to 0.2-0.4 mg/dL of conjugated bilirubin. The color change indicating a positive reaction, however, is a rather subtle transition among shades of beige, and sometimes is obscured by color inherent in the urine itself (e.g., marked hemoglobinuria). In such instances, confirmation of a suspected positive reaction is attempted using the Ictotest^® method.

Positive reactions

• Physiologic: Dogs have a low renal threshold for bilirubin, therefore highly concentrated urine samples from this species may have a trace to 1+ reaction. This may be clinically insignificant.
• Hepatobiliary disease: Detection of bilirubin in urine is generally an abnormal finding. Bilirubinuria generally results when conjugated bilirubin levels in blood are elevated as a result of hepatobiliary disease. In the dog, bilirubinuria may be seen prior to bilirubinemia due to the low renal threshold for bilirubin in this species. In all other species, bilirubinuria indicates cholestasis.
  In some cases of hemolytic anemia, bilirubinuria may be secondary to the hemolysis without any evidence of cholestasis. The renal tubular epithelium is capable of absorbing hemoglobin from the glomerular filtrate and converting it to conjugated bilirubin, which is then excreted in the urine. This will only occur with intravascular hemolysis, when free hemoglobin is filtered by the glomerulus.

• 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.
• Ascorbic acid: High concentrations of vitamin C inhibit the reaction.

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Last Updated: Friday, 15th January, 1999