Urine nitrites are produced when bacteria — primarily gram-negative organisms like E. coli — convert dietary nitrates (naturally present in urine) into nitrites. Normal urine does not contain nitrites, so a positive nitrite test strongly suggests bacterial infection in the urinary tract.
A positive nitrite result on a urine dipstick has high specificity for UTI and, combined with a positive leucocyte esterase result, provides a reliable point-of-care indication of bacterial infection. However, a negative result does not rule out UTI — some bacteria do not produce nitrites, and very rapid urine flow can prevent sufficient time for conversion. Urine nitrites are always interpreted alongside other urinalysis findings.
FAQs
If nitrites are negative, does that rule out UTI?
No. Enterococcus, Staphylococcus saprophyticus, and Pseudomonas do not produce nitrites. Negative nitrites with positive leucocytes and symptoms can still indicate UTI.
Why test first morning urine?
First morning urine has the longest bladder dwell time, allowing maximum nitrate-to-nitrite conversion and the highest test sensitivity.
Can you start antibiotics with positive nitrites without a culture?
For uncomplicated lower UTI in non-pregnant women, positive nitrites with symptoms often supports empirical treatment. Complicated UTIs should follow culture results.
Can diet affect nitrite testing?
Very low vegetable intake provides insufficient nitrate substrate, reducing test sensitivity. This is rarely clinically significant.
