Are nitrates present in urine during a urinary tract infection?

Are Nitrites Present During a UTI?

Nitrites are often—but not always—present in urine during a urinary tract infection, because nitrite formation requires specific bacterial enzymes, adequate dietary nitrate, and sufficient bladder dwell time (approximately 4 hours), all of which may be absent even in confirmed infections. 1, 2

How Nitrites Form in UTI

• Nitrite is produced when gram-negative bacteria (especially E. coli, Proteus, Klebsiella) metabolize dietary nitrates present in urine through bacterial nitrate reductase enzymes 1, 2
• This conversion requires the bacteria to remain in contact with urine for approximately 4 hours, explaining why frequent voiding reduces nitrite sensitivity 1, 2, 3
• Gram-positive organisms like Enterococcus and Staphylococcus saprophyticus lack nitrate reductase and cannot produce nitrite, resulting in nitrite-negative UTIs caused by these pathogens 4

Diagnostic Performance of Nitrite Testing

High Specificity, Poor Sensitivity

• Nitrite has excellent specificity (98-100%) but poor sensitivity (19-53%), meaning a positive result strongly indicates infection but a negative result does not rule it out 2, 3, 5
• In one study, only 3-5% of culture-proven Enterobacterales UTIs were nitrite-negative by dipstick, yet this still represents thousands of missed infections in clinical practice 6
• The combination of nitrite OR leukocyte esterase increases sensitivity to 93% while maintaining 96% specificity when both are positive 1, 2, 3

Why Nitrite Can Be Negative Despite Active Infection

• Insufficient bladder dwell time is the most common cause—young infants, children, and patients who void frequently cannot accumulate enough nitrite for detection 1, 2, 3
• Low dietary nitrate intake provides insufficient substrate for bacterial conversion, particularly in patients with restricted diets 6
• Dilute urine from high fluid intake reduces nitrite concentration below the detection threshold 6
• Gram-positive pathogens (Enterococcus, Staphylococcus saprophyticus) cause 10-20% of UTIs but cannot produce nitrite 4
• Exogenous interference from ascorbic acid (vitamin C) can cause false-negative results 6

Clinical Implications

When to Trust a Negative Nitrite

• A negative nitrite test does NOT exclude UTI—in febrile infants <2 years, urine culture is mandatory regardless of urinalysis results because 10-50% of culture-proven UTIs have false-negative urinalysis 2, 3
• Young infants have particularly poor nitrite sensitivity due to frequent voiding and short bladder dwell time 2, 3
• The negative predictive value of nitrite alone is insufficient to rule out infection in symptomatic patients 1, 7

When Nitrite Is Positive

• A positive nitrite result has 98% specificity and strongly indicates bacterial infection, justifying empiric treatment in symptomatic patients 2, 3
• When both leukocyte esterase AND nitrite are positive, specificity reaches 96% with combined sensitivity of 93%, making this one of the most reliable dipstick combinations 2, 3
• Positive nitrite should prompt urine culture collection before initiating antimicrobial therapy to guide definitive treatment 2, 3

Critical Pitfalls to Avoid

• Never rely on nitrite alone to rule out UTI—always combine with leukocyte esterase testing and clinical symptoms 1, 2, 7
• Do not adjust antibiotic selection based on nitrite results—nitrite-positive and nitrite-negative UTIs show no significant difference in antimicrobial resistance patterns to first-line agents 4, 8
• Recognize that nitrite-negative UTIs are common in specific populations: young children, patients with gram-positive infections, those with low dietary nitrate, and patients who void frequently 1, 2, 6
• The combination of negative leukocyte esterase AND negative nitrite effectively rules out UTI with 90.5% negative predictive value, but either test positive warrants further evaluation in symptomatic patients 2, 5, 7