Do Leukocytes with Nitrates in Urine Indicate UTI?
When both leukocyte esterase AND nitrite are positive on urinalysis, this combination has 96% specificity and 93% sensitivity for UTI, making it one of the most reliable dipstick combinations—but the diagnosis still requires clinical symptoms to distinguish true infection from asymptomatic bacteriuria. 1
Understanding the Diagnostic Performance
The combination of positive leukocyte esterase with positive nitrite is highly specific but must be interpreted in clinical context:
- Combined testing achieves 93% sensitivity and 96% specificity for UTI, representing the most accurate dipstick combination available 1, 2
- Nitrite alone has 98% specificity but only 53% sensitivity, meaning a positive result strongly suggests infection but a negative result cannot rule it out 1, 3
- Leukocyte esterase alone has 83% sensitivity and 78% specificity, making it more sensitive but less specific than nitrite 1, 2
The Critical Distinction: Symptoms Matter
The presence of both positive leukocyte esterase and nitrite does NOT automatically mean UTI requires treatment—you must assess for symptoms. 1, 2
When to Treat (True UTI):
- Positive dipstick PLUS acute urinary symptoms (dysuria, frequency, urgency, fever, or gross hematuria) indicates true UTI requiring treatment 1, 2
- The high specificity (96%) of combined positive tests justifies empiric antibiotic treatment while awaiting culture results in symptomatic patients 1
When NOT to Treat (Asymptomatic Bacteriuria):
- Positive dipstick WITHOUT symptoms represents asymptomatic bacteriuria, which should not be treated as it causes more harm than good by promoting antibiotic resistance 1, 2
- Asymptomatic bacteriuria prevalence is 15-50% in long-term care residents, making this distinction crucial 1, 2
Mandatory Next Steps
Always obtain urine culture before initiating antibiotics, as urinalysis cannot substitute for culture to document UTI and guide definitive therapy 1, 2:
- Culture results detect resistance patterns and confirm the diagnosis 1
- Process specimens within 1 hour at room temperature or 4 hours if refrigerated 2, 3
- Use proper collection methods: catheterization or suprapubic aspiration in infants/young children, midstream clean-catch in cooperative adults 1, 2
Important Limitations and Pitfalls
Nitrite Test Limitations:
- Requires approximately 4 hours of bladder dwell time to convert dietary nitrates to nitrites, explaining poor sensitivity in infants and patients who void frequently 1, 2
- Sensitivity is particularly low (19-53%) in pediatric populations due to frequent voiding 1, 3, 4
Collection Method Matters:
- Bagged urine specimens have 85% false-positive rates—always confirm with catheterized specimen before treating if the initial positive result came from a bagged specimen 1, 3
- Contaminated specimens produce false-positive leukocyte esterase results 2
Special Population Considerations:
Febrile infants <2 years:
- Obtain urine culture regardless of urinalysis results, as 10-50% of culture-proven UTIs have false-negative urinalysis 1, 2
- Young infants have particularly poor nitrite sensitivity due to frequent voiding 1, 2
Elderly and long-term care patients:
- Do not treat based on positive dipstick alone without specific urinary symptoms 1, 2
- Non-specific symptoms like confusion or functional decline alone should not trigger UTI treatment 2
Catheterized patients:
- Initiate empiric antibiotics only if symptomatic (fever, hemodynamic instability) and change the catheter before collecting the culture specimen 1, 2
Clinical Algorithm
- Assess for symptoms: dysuria, frequency, urgency, fever, or gross hematuria 1, 2
- If symptomatic: Obtain proper urine specimen and perform urinalysis 1, 2
- If both leukocyte esterase AND nitrite positive: Start empiric antibiotics after obtaining culture 1
- If asymptomatic: Do not pursue further testing or treatment regardless of positive dipstick 1, 2
- Always obtain culture before antibiotics to guide definitive therapy 1, 2