leukocyte esterase
Summary
An enzyme produced by neutrophils detected in urine via dipstick; a marker of pyuria (UTI). Positive result suggests bacterial infection but can have false positives and negatives.
Detail
Leukocyte esterase (LE) is a granulocytic enzyme produced primarily by neutrophils that is detected via urine dipstick as a surrogate marker for pyuria and urinary tract infection. A positive LE test correlates with >=5 WBCs per high-power field on microscopy and strongly suggests bacteriuria or UTI, particularly when accompanied by positive nitrites. However, LE has limitations: false positives occur with contamination, trichomonas, or tuberculosis; false negatives occur in early infections or very dilute urine. The presence of both LE and nitrites (>95% specificity for bacteriuria) warrants empiric antibiotic therapy in symptomatic patients. Confirmation by urine culture remains the gold standard.
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- Harrison's Principles of Internal Medicine
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