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Principle: A red azo compound is obtained in the presence of acid by the coupling of bilirubin with a diazonium salt.
Evaluation: The minimum sensitivity of the test strip is 0.5 to 1 mg bilirubin/dI urine. The colour fields correspond to the following values:
o (negative), 1 (+), 2 (++), 4 (+++) mg/dl or
0 (negative), 17 (+), 35 (++), 70 (+++) μmol/l.
Some urine components can produce a yellow colouration of the test strip. Ascorbic acid and nitrite in higher concentrations inhibit the test. Longer exposure of the urine to light leads to lowered, or falsely negative results. Higher, or falsely positive results can be caused by the presence of diagnostic or therapeutic dyes in the urine.
Diagnosis: Only conjugated (water soluble) bilirubin is excreted by the kidneys. Normally bilirubin is undetectable in urine. Bilirubinuria generally indicates liver parenchyma damage (e. g. acute virus hepatitis and other forms of hepatitis, liver cirrhosis, toxic liver cell damage) or biliary obstructions (e. g. cholangitis, obstructive jaundice). Unconjugated bilirubin, which is detectable in serum, indicating hemolytic jaundice is not excreted by the kidneys and is absent from urine.
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