Does a positive leukocyte esterase (leukoesterase) result in a urinalysis indicate a urinary tract infection (UTI)?

Leukocyte Esterase 2+ in Urinalysis and UTI Diagnosis

A 2+ leukocyte esterase result in urinalysis alone is not diagnostic of a urinary tract infection (UTI), but significantly increases the probability of infection when combined with clinical symptoms. 1

Diagnostic Value of Leukocyte Esterase

Leukocyte esterase is an enzyme produced by white blood cells and serves as a marker for pyuria (presence of white blood cells in urine). The diagnostic accuracy varies based on the test's intensity:

• Sensitivity of leukocyte esterase: 83-84% (range 67-94%)
• Specificity of leukocyte esterase: 78% (range 64-92%) 1

The interval likelihood ratio (ILR) for 2+ leukocyte esterase significantly increases the probability of UTI, with research showing an ILR of approximately 37.68 for 3+ results 2. This means a 2+ result substantially raises the pre-test probability of UTI, but is not definitive on its own.

Comprehensive UTI Diagnosis

For optimal diagnostic accuracy, consider:

1. Combined testing approach:

   • Leukocyte esterase + nitrite testing provides the highest diagnostic utility
   • Combined sensitivity: 93% (90-100%)
   • Combined negative predictive value: 95% 1

2. Clinical correlation is essential:

   • Symptoms (dysuria, frequency, urgency, fever)
   • Patient population (higher prevalence in certain groups)
   • Alternative diagnoses that can cause pyuria without infection 1

3. Confirmatory testing:

   • Urine microscopy for pyuria (>10 WBC/HPF significantly increases UTI probability)
   • Urine culture remains the gold standard 3

Special Considerations

• False positives: Non-infectious causes of pyuria, contamination from vaginal secretions, or certain medications can cause positive leukocyte esterase without infection 1

• Pathogen variability: Some organisms like Klebsiella spp. and Enterococcus spp. may cause UTI with less pronounced pyuria (53.3% and 52.0% positivity rates, respectively) compared to E. coli (80.6%) 4

• Pediatric populations: The American Academy of Pediatrics recommends both pyuria and positive urine culture for UTI diagnosis in children 1

Clinical Approach

1. For a patient with 2+ leukocyte esterase:

   • If symptomatic → high probability of UTI
   • If asymptomatic → consider other causes of pyuria

2. Increase diagnostic certainty by checking:

   • Nitrite test (high specificity at 98%)
   • Microscopic examination for WBCs and bacteria
   • Urine culture when diagnosis is uncertain 1, 5

3. Treatment decisions:

   • Antibiotics should only be used when both positive urinalysis findings AND clinical symptoms are present
   • Avoid treating asymptomatic bacteriuria 1

Common Pitfalls to Avoid

• Treating based solely on leukocyte esterase without considering clinical context
• Ignoring the possibility of false positives from contamination
• Failing to consider pathogen variability in pyuria presentation
• Not obtaining cultures in complicated cases or when diagnosis is uncertain

Remember that while a 2+ leukocyte esterase significantly increases the probability of UTI, it must be interpreted within the clinical context and ideally confirmed with additional testing for definitive diagnosis.