A nitrite test is a standard component of a urinary test strip. A positive test for nitrites in the urine is called nitrituria.
This test is commonly used in diagnosing urinary tract infections (UTIs).  A positive nitrite test indicates that the cause of the UTI is a Gram-negative organism, most commonly Escherichia coli.  The reason for nitrites' existence in the presence of a UTI is due to a bacterial conversion of endogenous nitrates to nitrites.  This may be a sign of infection.  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.
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.  In addition, a nitrite test does not detect organisms unable to reduce nitrate to nitrite, such as enterococci, staphylococci (Staphylococcus saprophyticus), Acinetobacter, or adenovirus.