Principle: The test is based on the esterase activity of granulocytes. This enzyme splits a carboxylic acid ester. The alcohol component formed during this step reacts with a diazonium salt to form a violet dye.
Evaluation: The test detects values from about 10 to 25 leukocytes/l urine. Discolourations, which can no longer be correlated to the negative test field, and weakly violet discolourations after 120 seconds are to be considered positive. The colour fields correspond to the following leukocyte concentrations:
negative (normal), 25, 75, 500 leukocytes/μl
A diminished reaction can result for protein excretion above 500 mg/dl, and a glucose concentration above 2 g/dl as well as during therapy with preparations containing cephalexin or gentamycin. Bacteria, trichomonades and erythrocytes do not give a positive reaction with this test. Formaldehyde (a preservative) can cause falsely positive reactions. Excretion of bilirubin, nitrofurantoin, or other strongly coloured compounds can cover the reaction colour. For samples from female patients vaginal secretion can simulate a falsely positive reaction. In order to avoid falsely positive results, the urine should only be sampled after thorough cleaning of the genitals.
Diagnosis: An increased excretion of leukocytes in urine (leukocyturia) is an important symptom for infectious diseases of the kidneys and/or urinary tract (incl. the prostate). Leukocyturia is especially important for diagnosis of chronic pyelonephritis. Often it is the only symptom between acute attacks. Other causes for leukocyturia may be: analgetic nephropathia, glomerulopathia and intoxications, cystitis, urethritis, kidney or urogenital tuberculosis, fungus and trichomonade infections, gonorrhoea, urolithiasis, tumors with obstructions.