Is a +1 leukocyte (white blood cell) esterase result indicative of a urinary tract infection (UTI)?

Leukocyte Esterase +1 Is Not Diagnostic of UTI by Itself

A +1 leukocyte esterase result alone is not sufficient to diagnose a urinary tract infection (UTI) and should not be treated without additional clinical symptoms and confirmatory testing. 1

Understanding Leukocyte Esterase in Urinalysis

Leukocyte esterase (LE) is an enzyme released from white blood cells that serves as a surrogate marker for pyuria (presence of white blood cells in urine). While it can indicate inflammation in the urinary tract, its presence alone does not confirm infection.

The diagnostic value of LE testing:

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

This means that while LE testing is reasonably sensitive, it still produces false positives in approximately 22% of cases.

Proper Diagnostic Approach for UTI

Required Elements for UTI Diagnosis:

1. Clinical symptoms (fever, dysuria, gross hematuria, new/worsening urinary incontinence)
2. Laboratory findings:
   • Positive leukocyte esterase or nitrite test
   • Microscopic examination showing ≥10 WBCs/high-power field
   • Positive urine culture with significant bacterial growth

The Infectious Diseases Society of America strongly recommends that:

• Urinalysis and urine cultures should not be performed for asymptomatic individuals 2, 1
• Diagnostic evaluation should be reserved for those with acute onset of UTI-associated symptoms 2
• If pyuria (≥10 WBCs/high-power field) or positive leukocyte esterase/nitrite test is present, only then should a urine culture be ordered 2

Improved Diagnostic Accuracy:

• Combined testing: Using leukocyte esterase together with nitrite testing improves diagnostic accuracy (sensitivity 93%, specificity 72%) 1
• Microscopic examination: Generally more accurate than dipstick testing alone 1

Common Pitfalls to Avoid

1. Treating asymptomatic bacteriuria or isolated pyuria: This increases antibiotic resistance without clinical benefit, especially in elderly patients 1

2. Relying solely on dipstick results: A study by Dalton (2000) found a lack of sensitivity for leukocyte esterase as an indicator of UTI 3

3. Specimen contamination: Urogenital flora in a urine culture typically indicates specimen contamination during collection rather than true infection 1

4. Delayed processing: Specimens should be processed within 1-4 hours to preserve accuracy 1

Special Populations

For most patients, a +1 leukocyte esterase result without symptoms should not be treated. However, certain populations require special consideration:

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

• Immunocompromised patients: May require treatment even with minimal findings 1

• Elderly in long-term care facilities: The Infectious Diseases Society of America strongly recommends against performing urinalysis and urine cultures for asymptomatic residents 2, 1

In conclusion, while leukocyte esterase testing is a valuable screening tool, a +1 result alone is insufficient for UTI diagnosis and should be interpreted in the context of clinical symptoms and additional laboratory findings.