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Principle: Microorganisms, which are able to reduce nitrate to nitrite, are indicated indirectly with this test, which is based on the principle of Griess reagent. The test paper contains an amine and a coupling component. Diazotization and subsequent coupling result in a red coloured azo compound. Only nitrite can produce a diazonium salt for coupling reaction, therefore falsely positive results are virtually impossible in this case.
Evaluation: The test detects concentrations from 0.05 to 0.1 mg nitrite/dl urine. Any pink colour indicates a bacterial infection of the urinary tract. The colour intensity only shows the nitrite concentration, and does therefore not provide information about the extent of the infection. A negative result does not preclude an infection of the urinary tract, if bacteria, which cannot produce nitrite are present. Falsely negative results can be produced by high doses of ascorbic acid, by antibiotics therapy, and by very low nitrate concentrations in urine as the result of low nitrate diet or strong dilution (diuresis). Falsely positive results can be caused by the presence of diagnostic or therapeutic dyes in the urine.
Diagnosis: Bacteria, which cause infections, and can produce nitrite in the urine are e. g. E. coli (bacteria which causes most frequently infections), Aerobacteria, Citrobacteria, Klebsiella, Proteus, Salmonellae and in part Enterococci, Pseudomonas and Staphylococci. If the test is positive a microscopic examination and determination of susceptibility of pathogenic bacteria to chemotherapeutic agents should follow.
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