What does a positive leukocyte esterase (LE) and negative nitrite test indicate in a patient with symptoms of a urinary tract infection (UTI)?

Interpreting Positive Leukocyte Esterase with Negative Nitrite in UTI Diagnosis

A positive leukocyte esterase test with a negative nitrite test in a patient with UTI symptoms suggests pyuria without bacterial nitrate reduction and requires urine culture confirmation before treatment, as this pattern has moderate diagnostic value with approximately 79% positive predictive value for UTI but does not definitively confirm infection. 1

Diagnostic Significance of LE+/Nitrite- Pattern

Sensitivity and Specificity

• Leukocyte esterase test:
  • Sensitivity: 83-94% (higher in symptomatic patients)
  • Specificity: 78-94% 1
• Nitrite test:
  • Sensitivity: Only 53% (range 15-82%)
  • Specificity: 98% (range 90-100%) 1

Clinical Interpretation

1. Pyuria Present: Positive leukocyte esterase indicates the presence of white blood cells in urine (pyuria) 1
2. Possible Causes:
   • Early UTI where bacteria haven't had sufficient time (4+ hours) to convert nitrates to nitrites 1
   • Infection with non-nitrate-reducing organisms (e.g., Staphylococcus saprophyticus, Enterococcus)
   • Frequent urination preventing bacterial accumulation needed for nitrite detection
   • Low urinary nitrate levels due to dietary factors 1

Management Algorithm

For Symptomatic Patients:

1. With classic UTI symptoms (dysuria, frequency, urgency):

   • Obtain urine culture
   • Consider empiric antibiotic treatment while awaiting culture results 1

2. With atypical or mild symptoms:

   • Obtain urine culture before initiating antibiotics
   • Consider withholding antibiotics until culture results if symptoms are mild 1

For Asymptomatic Patients:

• Do not treat based on dipstick results alone
• Positive LE with negative nitrite has lower predictive value in asymptomatic individuals 1
• Consider asymptomatic bacteriuria, which generally should not be treated except in pregnancy 1

Important Clinical Considerations

Age-Related Factors

• In children: Nitrite test has particularly low sensitivity as they empty bladders frequently 1
• In elderly patients: Dipstick specificity ranges from 20-70%, with negative results for both tests often suggesting absence of UTI 1

Sample Collection Matters

• Fresh urine samples (≤1 hour at room temperature or ≤4 hours refrigerated) are essential for accurate results 1
• Collection method affects reliability:
  • Catheterized specimens have higher specificity than bag specimens 1
  • False positives more common with bag collection 1

Diagnostic Pitfalls to Avoid

1. Don't rule out UTI with negative nitrite alone (sensitivity only 53%) 1
2. Don't diagnose UTI based solely on positive leukocyte esterase without culture confirmation 1, 2
3. Don't miss asymptomatic bacteriuria in pregnant women (requires culture confirmation despite dipstick results) 3
4. Don't assume all pyuria represents infection - sterile pyuria can occur with other inflammatory conditions 1

Bottom Line

A small amount of leukocyte esterase with negative nitrite represents an intermediate risk for UTI that requires clinical correlation and culture confirmation. The combination has moderate diagnostic value but is insufficient to definitively diagnose or exclude UTI, particularly in high-risk populations.