At least 4h – this is often not the case in practice; most frequently found in morning urine samples
Written sources: European Urinanalysis Guidelines; Scan. J. Clin. Lab. Invest., 2000; 60:1-96: Urine should be stored in the bladder for a duration of 4-8h. This is essential to ensure sufficient nitrite accumulation in urine for detection with the dipstick method, and hence, with our test.
Therefore, few positive nitrite tests are expected in practice if morning urine samples are not used. Since UTI somewhat increases urinary frequency, the urine does not often stay long enough in the bladder.
ARESC Study, Naber, 2008: In practice, only 30% of female patients with bacteriuria yield positive results for nitrite.
Inhibitors – high concentrations of Vitamin C; antibiotics treatment
UTI due to non-nitrite producing bacteria or other microorganisms– very rare – the vast majority of UTIs are caused by E.coli
Low-nitrite diet – very rare
Stale urine - Further reaction of nitrite to nitrogen.
In practice, not often to be expected, since urine samples are usually processed within reasonable time to avoid such reactions.
With TENA U-test this is basically impossible since urine is taken up by the test immediately when voided by the patient and chemical reaction starts as soon as urine enters test card – no alteration – no further reaction of nitrite present in urine.
Other causes for the presence of leukocytes – e.g. another type of infection or reason for inflammation – definitely needs further examination by a doctor
MEASURE: repetition of test using morning urine sample
For TENA U-test: if leukocyte indicator does show a positive result consider this as indication for further evaluation and information to the doctor to get instructions on further measures