The Effect of Time Passage on False Positive Urinary Nitrite Test

Urinary tract infection is one of the most prevalent pediatric diseases which, if diagnosed and treated promptly, can lead to potential severe sequelae. Positive urinary nitrite is a sensitive test to determine urinary tract infection. In this study we evaluate the effect of delayed urinalysis on the result of urinary nitrite. We studied mid-stream clean catch urine of 30 children in Imam Sajjad Hospital of Yasouj University of Medical Sciences. Specimens stored at room temperature and urinary nitrite measured at 0, 0.5, 1 3 and 6 hours after collection. All specimens revealed negative urinary nitrite on beginning. 10% of specimens (3 cases) became nitrite positive between 30 minutes until 6 hours after collection. These false positive results of urinary nitrite were shown to have no relationship with urine culture and therefore no relativity to urinary tract infection. 3 reported positive cultures were not the same specimens with positive urinary nitrite and were related to non-nitrite positive organisms. We conclude that with passage of time after urine collection urinary nitrite may become falsely positive and lead to over-diagnosis of urinary tract infection. Therefore, all collected specimens must be transferred to laboratory as soon as possible to avoid false positive values.