Can a patient with a positive nitrite test but negative leukocyte (white blood cell) test still have a urinary tract infection (UTI)?

Positive Nitrite with Negative Leukocytes Can Still Indicate a UTI

A positive nitrite test with negative leukocytes can still indicate a urinary tract infection (UTI), and should be considered clinically significant, especially when accompanied by symptoms. 1

Diagnostic Value of Nitrite and Leukocyte Tests

Nitrite Test Characteristics

• Highly specific (98%, range 90-100%) but less sensitive (53%, range 15-82%) for UTI 1
• Positive nitrite indicates bacterial conversion of dietary nitrates to nitrites, requiring approximately 4 hours of bladder incubation time 1
• False negatives are common due to:
  • Frequent urination (insufficient time for nitrate conversion) 2
  • Non-nitrate-reducing organisms (e.g., Enterococcus) 3
  • Dilute urine or low dietary nitrate intake 1

Leukocyte Esterase Test Characteristics

• More sensitive (83%, range 67-94%) but less specific (78%, range 64-92%) than nitrite 1
• Indicates pyuria (presence of white blood cells in urine) 1
• Absence of leukocyte esterase in the presence of bacteria may indicate asymptomatic bacteriuria rather than true infection 1

Clinical Interpretation of Positive Nitrite/Negative Leukocyte Results

Possible Explanations

1. Early UTI: Bacterial presence before significant inflammatory response 1
2. Asymptomatic bacteriuria: Bacterial colonization without infection 1
3. Non-pyogenic infection: Some pathogens cause less pyuria 1, 3
4. Organism-specific patterns: Enterococcus infections (always nitrite negative) account for only 3.2% of nitrite-negative UTIs 3

Clinical Approach

• When nitrite is positive but leukocytes are negative:
  • Consider the result clinically significant, especially with symptoms 1, 4
  • Obtain urine culture to confirm infection and identify the pathogen 1
  • Consider empiric treatment while awaiting culture results if symptoms are present 4

Diagnostic Accuracy of Combined Testing

• Combined testing improves diagnostic accuracy:
  • Either leukocyte esterase OR nitrite positive: Sensitivity 93% (90-100%), Specificity 72% (58-91%) 1
  • Both leukocyte esterase AND nitrite positive: Highest specificity for UTI 1, 5
  • Bayesian analysis suggests nitrite has higher true specificity (97.7%) than traditional estimates 6

Recommendations for Clinical Practice

• Do not rule out UTI based solely on negative leukocyte test when nitrite is positive 1, 4
• Obtain urine culture for definitive diagnosis, especially in high-risk populations 1
• Consider patient symptoms and risk factors alongside test results 1
• In symptomatic patients with positive nitrite but negative leukocytes, empiric treatment while awaiting culture results is reasonable 4

Special Considerations

• In children, nitrite testing is less sensitive due to frequent voiding 1
• First morning urine specimens may improve nitrite test sensitivity 2
• Automated urinalysis methods correlate well with manual methods and may provide more standardized results 1
• False positive nitrite results are uncommon (specificity 98%), making a positive result clinically meaningful 1, 6