Nitrite test strips do not replace the traditional urine culture for the identification and quantitation of bacteria.  Nitrite reagent strips provide a rapid, economical means of detecting significant bacteriuria caused by nitrate-reducing bacteria.  The most common infecting microorganism in urinary infection is Escherichia coli followed by Klebsiella species, Enterobacter species, Proteus species.  Since the test strip uses reducing reaction method of nitrate to nitrite in Gram-negative bacteria, if a person has injected with antibiotics or bacterial infection which does not reduce to nitrite, it will result in a false negative.

Following factors affect nitrite formation and detections and lead to false negatives:

A.       When the infecting microbe is not a nitrate-reducer 

B.       Inadequate dietary amounts of nitrate 

C.       Inadequate bladder retention time (a minimum of 4 hours for the bacterial conversion)