Nitrite test

A positive test for nitrite is indicated by a dark brown solution, arising from the iron-nitric oxide complex ion.

[1] A common method of quantitative nitrite detection is the Griess test, which relies on the reaction of nitrite with the two components of a Griess reagent to form a red azo dye.

A positive nitrite test indicates that the cause of the UTI is a Gram-negative organism, most commonly Escherichia coli.

However, other parameters, such as leukocyte esterase, urine white blood cell count, and symptoms such as dysuria, urinary urgency, fevers, and chills must be correlated to diagnose an infection.

[3] False-negative nitrite tests in urinary tract infections occur in cases with a low colony forming unit (CFU) count, or in recently voided or dilute urine.