What is the significance of leukocyte esterase presence in urine?

Significance of Leukocyte Esterase Presence in Urine

Leukocyte esterase (LE) in urine is a valuable screening marker for urinary tract infection (UTI) with high sensitivity (77-84%) but moderate specificity (78-91%), making it most useful when combined with other clinical findings and tests. 1

Diagnostic Value of Leukocyte Esterase

Accuracy Metrics

• Sensitivity: 77-84% (detects most UTIs but has false negatives)
• Specificity: 78-91% (moderate false positive rate)
• When combined with nitrite testing:
  • Either test positive: Sensitivity increases to 93-94%
  • Both tests positive: Specificity increases to 96% 1

Mechanism and Interpretation

• Leukocyte esterase is an enzyme released from white blood cells (leukocytes) in urine
• Indicates pyuria (presence of white blood cells in urine)
• Detected through dipstick testing, which is rapid and simple 2
• A negative LE test has excellent negative predictive value, helping to exclude UTI 3

Clinical Significance and Decision-Making

Positive LE Test

• Suggests inflammation in the urinary tract
• May indicate UTI but requires clinical correlation
• Can be present in both infectious and non-infectious inflammatory conditions 1
• In symptomatic patients with positive LE, empiric treatment may be appropriate while awaiting culture results

False Positives

• Common causes:
  • Non-infectious inflammatory conditions
  • Vulvovaginitis (especially in prepubertal girls) 4
  • Phimosis in boys 4
  • Contamination during collection

False Negatives

• May occur with:
  • Early infection
  • Certain antibiotics
  • Neutropenia 3
  • High urinary glucose or protein
  • Vitamin C ingestion

Optimal Use in Clinical Practice

Recommended Testing Algorithm

1. Use LE testing as an initial screening tool
2. Combine with nitrite testing for improved accuracy
3. Consider urine microscopy for confirmation of pyuria
4. Obtain urine culture in:
   • Symptomatic patients with positive LE
   • Patients with fever and suspected UTI
   • High-risk populations (pregnant women, immunocompromised)
   • Suspected urosepsis 3

Special Populations

• Elderly patients in long-term care facilities:

  • High prevalence of asymptomatic bacteriuria (10-50%)
  • Absence of pyuria can exclude bacteriuria with high negative predictive value
  • Presence of pyuria alone has low positive predictive value 3

• Pregnant women:

  • Asymptomatic bacteriuria should always be treated due to increased risk of pyelonephritis and pregnancy complications 1

Important Caveats

• LE testing alone is insufficient for definitive UTI diagnosis

• Urine culture remains the gold standard for confirming UTI 1

• Asymptomatic bacteriuria should be distinguished from true UTI

• Treatment decisions should consider:

  • Presence of symptoms
  • Patient risk factors
  • Results of additional testing (nitrite, microscopy, culture)

• Common pitfall: Treating asymptomatic patients with positive LE test alone, which may lead to unnecessary antibiotic use and potential resistance 1