What does the presence of leukocyte esterase and blood in urine indicate?

Leukocyte Esterase and Blood in Urine: Diagnostic Significance

The presence of leukocyte esterase and blood in urine most commonly indicates a urinary tract infection (UTI), especially when accompanied by symptoms such as dysuria, frequency, urgency, or suprapubic pain. 1 However, this finding requires careful interpretation as it may also indicate other conditions depending on clinical context.

Diagnostic Interpretation

Symptomatic Patients

When leukocyte esterase and blood are found in urine of patients with urinary symptoms:

• Primary indication: Urinary tract infection

  • Combined leukocyte esterase and nitrite testing provides the highest diagnostic accuracy for UTI with a sensitivity of 93% and specificity of 72% 1
  • Leukocyte esterase alone has a sensitivity of 83% but lower specificity of 78% 1
  • The presence of pyuria (≥10 WBCs/high-power field) with positive leukocyte esterase warrants urine culture 2

• Other potential causes:

  • Glomerulonephritis (if accompanied by proteinuria >2+, red blood cell casts, and deformed red blood cells) 2
  • Kidney stones
  • Interstitial cystitis
  • Urinary tract trauma

Asymptomatic Patients

In asymptomatic individuals, these findings should be interpreted cautiously:

• Asymptomatic bacteriuria with pyuria is common, especially in elderly patients, and generally does not require treatment 2, 1
• The Infectious Diseases Society of America strongly recommends against performing urinalysis and urine cultures for asymptomatic residents in long-term care facilities 2

Clinical Approach

1. Assess for symptoms:

   • Typical UTI symptoms: dysuria, frequency, urgency, suprapubic pain
   • In elderly: may include new-onset confusion, incontinence, or anorexia 1

2. Confirm findings:

   • Microscopic examination for WBCs (pyuria defined as ≥10 WBCs/high-power field) 2
   • Urine culture only if leukocyte esterase or nitrite positive 2, 1

3. Management decisions:

   • Symptomatic patients: Consider empiric antibiotic therapy while awaiting culture results 1
   • Asymptomatic patients: No treatment indicated; monitoring only 2, 1
   • Special populations: Pregnant women with asymptomatic bacteriuria should be treated due to increased risk of complications 1

Important Considerations

• The combination of positive leukocyte esterase and nitrite has higher diagnostic value than either test alone 1, 3
• Proper specimen collection is crucial to avoid contamination:
  • Clean-catch mid-stream specimens are preferred 1
  • For elderly patients who cannot provide clean-catch specimens, in-and-out catheterization may be necessary 2
• Specimens should be processed within 1 hour at room temperature or within 4 hours if refrigerated to preserve accuracy 1

Common Pitfalls to Avoid

• Overtreatment: Treating asymptomatic bacteriuria or pyuria increases antibiotic resistance without clinical benefit 1
• Misattribution: Non-specific symptoms in elderly patients are often incorrectly attributed to UTI when other causes may be responsible 1
• Inadequate testing: Relying solely on dipstick without microscopy can lead to false positives; combined testing improves diagnostic accuracy 1, 4
• Improper specimen handling: Delayed processing can lead to false negatives or positives 1

Remember that while leukocyte esterase and blood in urine often suggest UTI, clinical correlation is essential for proper diagnosis and management.