Urine Nitrites
Urine Nitrites· also: Nitrituria, Urine Nitrtes
Clinical Overview
Urine nitrites are produced by bacterial reduction of dietary nitrates to nitrites — a metabolic activity of most Gram-negative bacteria (E. coli, Klebsiella, Proteus, Enterobacter). A positive urine nitrite on dipstick indicates the presence of bacteria that can perform this conversion and strongly suggests urinary tract infection. When positive nitrites are combined with positive leukocytes (white blood cells), the specificity for UTI approaches 95%.
Why This Test Matters
Urine nitrites are a rapid, inexpensive screening test for bacterial UTI. The sensitivity of nitrites alone for UTI is 45–60% — it misses infections caused by organisms that cannot reduce nitrates (Staphylococcus saprophyticus, Enterococcus, Pseudomonas — common UTI pathogens). A negative nitrite result does NOT rule out UTI. The full urinalysis dipstick should always be interpreted as a combination: nitrites + leukocytes + leukocyte esterase together provide better diagnostic accuracy than any marker alone. In symptomatic patients with a classic UTI presentation (dysuria, frequency, urgency, suprapubic pain), empirical antibiotics are appropriate regardless of dipstick result — clinical diagnosis drives management in uncomplicated UTI. Urine culture and sensitivity testing should be obtained before antibiotics in complicated UTI (men, pregnant women, catheterized patients, recurrent infections, suspected pyelonephritis).
Reference RangesWHO/IFCC standards
| Reference Range | Unit | Notes |
|---|---|---|
| Negative / Non-reactive | qualitative | Negative = normal; Positive = bacteria likely present |
What Causes Abnormal Results?
High Urine Nitrites Causes
- UTI caused by nitrate-reducing Gram-negative bacteria: E. coli (most common cause of UTI), Klebsiella pneumoniae, Proteus mirabilis, Enterobacter, Salmonella
- Asymptomatic bacteriuria (especially in elderly and pregnant women)
Low Urine Nitrites Causes
- Negative nitrites do not exclude UTI — organisms that do not reduce nitrates (Enterococcus, Staphylococcus saprophyticus, Candida, Pseudomonas) cause UTI with negative nitrite
- Insufficient bladder dwell time (<4 hours between voids — nitrate not converted if urine passes through too quickly)
- Low dietary nitrate intake
Signs & Symptoms to Watch For
How to Prepare for This Test
The best sample for nitrite testing is first morning urine (urine has been in the bladder for several hours — sufficient dwell time for bacterial conversion). Midstream clean catch is required. Refrigerate and test within 2 hours — bacteria proliferate at room temperature, producing false-positive results.
Factors That Can Affect Results
- Short bladder dwell time (<4 hours) — insufficient time for bacteria to convert nitrate to nitrite
- High vitamin C (ascorbic acid) concentration — inhibits nitrite dipstick reaction (false negative)
- Organisms that cannot reduce nitrate (Enterococcus, Staphylococcus saprophyticus, Candida) — cause UTI with negative nitrite
- Dilute urine (low specific gravity) may decrease nitrite concentration below detection threshold
- Contamination of the urine sample (bacteria from skin flora convert nitrate — false positive)
Related Topics
Frequently Asked Questions
My urine nitrites are negative but I have UTI symptoms — do I still have a UTI?
Yes, you may well have a UTI. The nitrite test has a sensitivity of only 45–60% — it misses 40–55% of true UTIs. Common organisms like Enterococcus and Staphylococcus saprophyticus (frequent cause of UTI in young sexually active women) do not reduce nitrates and give a negative nitrite result. If you have classic UTI symptoms (dysuria, frequency, urgency) but a negative nitrite, look at the leukocyte esterase and white blood cells — these are the more sensitive markers for inflammation. A symptomatic woman with leukocyte esterase positive but nitrite negative still has approximately a 70–80% likelihood of UTI and empirical treatment is appropriate.
Should asymptomatic bacteriuria (positive nitrites without symptoms) always be treated?
No — most asymptomatic bacteriuria should NOT be treated with antibiotics. Exceptions where treatment IS recommended: (1) Pregnant women — asymptomatic bacteriuria in pregnancy is associated with pyelonephritis and preterm birth; treat after urine culture. (2) Before urological procedures that may cause mucosal bleeding. In all other situations — including elderly patients, catheterized patients, and diabetics — asymptomatic bacteriuria does not benefit from antibiotic treatment and treating it promotes antimicrobial resistance. Only symptomatic UTI should be treated in these groups.