Urine Diagnostics / Urine Test Strips / Portfolio Urine Test Strips / Bilirubin
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| Test principle | |
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The test is based on the coupling of bilirubin with stabilised diazonium salt in a highly acidic medium. The reaction is independent of the pH value of the urine. |
| Sensitivity |
| The practical sensitivity in ascorbic acid free urine is 0.6 mg/dl (10 µmol/l) |
| Sources of errors |
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False-negative results: Diminished or negative results can occur due to high concentrations of vitamin C or nitrite. Bilirubin is just as sensitive to light as urobilinogen, so standing in light for a long time can result in diminished or negative results. Direct sunlight causes oxidation of the bilirubin. Urine for bilirubin determination must be protected from light. Urines should not be filtered or centrifuged, as precipitations of calcium salts can adsorb bilirubin. False-positive results: Pharmaco-metabolites (e.g. phenazopyridines), which produce coloration at low pH, can cause false-positive results. Increased urobilinogen concentrations can amplify the sensitivity of the bilirubin test pad. |
| Clinical significance |
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Bilirubin is produced as a degradation product of haemoglobin in the reticuloendothelial system, in the milt and in Kupffer's star cells of the liver as a result of physiological erythrocytolysis.This free bilirubin, insoluble in water, bonds with serum albumin and pass with the blood to the liver. In the liver, the bilirubin is mainly converted into water soluble bilirubin glucuronide by coupling with glucuronic acid (effected by the enzyme glucoronyl transferase). The water soluble conjugated bilirubin is eliminated via the bile into the intestine. The disordered metabolism caused by liver bile diseases, causes large quantities of water soluble bilirubin glucuronide to pass via the blood into the kidneys and to appear in the urine.Values from 5 mg bilirubin/l lead to a reddish-orange peach colour and indicate the early stages of liver disease.
Bilirubin cannot normally be detected in urine. Haemolytic jaundice (icterus) causes overproduction of bilirubin, only the water insoluble, unconjugated bilirubin is increased in the blood (from around 2 mg bilirubin/100 ml serum; 34 µmol bilirubin/l serum). Bilirubin reacts with the elastic fibres of the skin and therefore causes the yellow colouration. Then, bilirubin can not be detected in the urine. |
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