Is a urinary tract infection (UTI) likely with a urinalysis showing positive nitrates and negative leukocyte esterase?

Positive Nitrites with Negative Leukocyte Esterase: UTI Diagnosis

A positive nitrite test with negative leukocyte esterase strongly suggests a urinary tract infection (UTI) if the patient has urinary symptoms, as nitrites have excellent specificity (98-100%) for detecting bacteriuria. 1, 2

Diagnostic Interpretation

The combination of positive nitrites and negative leukocyte esterase is uncommon but clinically significant:

• Nitrites have very high specificity (98-100%) but poor sensitivity (19-53%) for UTI, meaning a positive result strongly indicates bacterial presence even when other markers are negative 1, 2, 3

• The negative leukocyte esterase does not rule out infection in this scenario, as leukocyte esterase has only moderate sensitivity (83%) and can be falsely negative in early infections or with rapid urine transit 2, 3

• This pattern can occur when bacteria are present but the inflammatory response is minimal or early, particularly in patients who void frequently (shorter bladder dwell time) or in early-stage infections 1, 2

Clinical Decision Algorithm

If the patient has urinary symptoms (dysuria, frequency, urgency, fever, or gross hematuria):

• Treat as UTI - the positive nitrite with symptoms is sufficient for diagnosis in uncomplicated cases 1, 2
• Obtain urine culture before starting antibiotics to guide therapy if needed 2, 4
• Empiric antibiotics are appropriate while awaiting culture results 1, 2

If the patient is asymptomatic:

• Do not treat - this likely represents asymptomatic bacteriuria, which should not be treated in most populations 2, 3
• No further testing is indicated unless the patient is pregnant or undergoing urologic procedures 2

Important Clinical Considerations

Avoid the common pitfall of dismissing positive nitrites due to negative leukocyte esterase:

• Research shows that when both nitrite and leukocyte esterase are negative, approximately 50% of samples can still be culture-positive, demonstrating that no single test is perfect 5
• The specificity of nitrites (94-100%) means false positives are rare, making a positive result clinically meaningful 1, 5, 6

Special populations require modified interpretation:

• In elderly or long-term care residents, only treat if specific urinary symptoms are present (not confusion or falls alone), as asymptomatic bacteriuria prevalence is 15-50% 1, 2
• In catheterized patients, bacteriuria is nearly universal; treat only with fever, hypotension, or specific urinary symptoms 2, 4
• In febrile infants and children, always obtain urine culture before treatment regardless of dipstick results 1, 2, 4

Specimen Quality Matters

• Ensure proper specimen collection (midstream clean-catch or catheterization) to avoid contamination that could cause false-positive nitrites 2, 3
• Process specimens within 1 hour at room temperature or 4 hours if refrigerated, as bacterial overgrowth can produce false-positive nitrites 3