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Quick Reference
  • Normal Result: Negative
  • Positive Result: Indicates presence of white blood cells in urine (pyuria)
  • Sensitivity for UTI: 75-96%
  • Specificity for UTI: 94-98% (when combined with nitrites)
  • Primary Use: Screening test for urinary tract infection and urinary inflammation
  • Sample Type: Fresh urine specimen (midstream clean catch)
  • Key Point: Positive leukocyte esterase + positive nitrites = high probability of bacterial UTI

Test Description

Leukocyte esterase is an enzyme produced by white blood cells, specifically neutrophils. The urinalysis dipstick test detects this esterase enzyme, which is released when neutrophils lyse (break down) in urine. The presence of leukocyte esterase indicates pyuria, the presence of white blood cells in urine, which is a hallmark of urinary tract inflammation or infection.

This test serves as a rapid, cost-effective screening tool for urinary tract infections (UTIs) and other inflammatory conditions affecting the urinary system. Unlike microscopic examination that requires laboratory processing, the leukocyte esterase dipstick provides immediate results at the point of care.

What the Test Detects

  • Esterase enzyme: Released from lysed neutrophils in urine
  • Pyuria: Presence of white blood cells (typically ≥10 WBCs per high-power field on microscopy)
  • Granulocyte activity: Indicates active inflammatory response in urinary tract

Clinical Importance

  • High sensitivity: Effective screening test for UTI with 75-96% sensitivity
  • Point-of-care testing: Provides rapid results without microscopy
  • Cost-effective: Inexpensive first-line screening tool
  • Guides treatment: Helps determine need for empiric antibiotic therapy
Clinical Significance

Conditions Causing Positive Leukocyte Esterase

A positive leukocyte esterase test indicates pyuria (WBCs in urine), which can result from various infectious and non-infectious causes.

Infectious Causes

  • Urinary tract infection (UTI): Most common cause, including cystitis and pyelonephritis
  • Pyelonephritis: Upper urinary tract infection involving the kidneys
  • Sexually transmitted infections (STIs): Chlamydia, gonorrhea causing urethritis
  • Prostatitis: Bacterial infection of the prostate gland
  • Urethritis: Inflammation of the urethra from various pathogens

Non-Infectious Inflammatory Causes

  • Interstitial nephritis: Drug-induced or autoimmune kidney inflammation
  • Glomerulonephritis: Inflammatory kidney disease affecting glomeruli
  • Renal calculi (kidney stones): Stones causing inflammation and tissue damage
  • Chronic kidney disease: Various causes of ongoing renal inflammation
  • Bladder tumors: Malignancy causing local inflammation
  • Appendicitis: Adjacent inflammation affecting bladder

Sterile Pyuria (LE positive, culture negative)

  • Tuberculosis: Mycobacterial infection not detected on routine culture
  • Fungal infections: Candida or other fungi requiring special culture media
  • Prior antibiotic treatment: Partially treated bacterial infection
  • Fastidious organisms: Bacteria not growing on standard culture media
  • Urethritis from STIs: Chlamydia, Ureaplasma requiring special testing

Clinical Interpretation Patterns

Swipe to see more
LE Result Nitrites Interpretation Likelihood of UTI
Positive Positive High probability bacterial UTI ~95% specific
Positive Negative Possible UTI (non-E. coli) or sterile pyuria Common - requires clinical correlation
Negative Positive Possible UTI (uncommon pattern) Consider contamination or early infection
Negative Negative Low probability of UTI High negative predictive value
Interfering Factors

False Positive Results

Conditions that can cause a positive leukocyte esterase without true urinary tract pathology:

  • Sample contamination: Vaginal secretions, skin flora, or improper collection technique
  • Vaginal white blood cells: Menstruation, vaginal infections, or cervicitis
  • Trichomonas infection: Vaginal trichomoniasis contaminating urine specimen
  • Histiocytes: Can trigger positive reaction on dipstick
  • Medications: Imipenem, meropenem (some formulations), nitrofurantoin metabolites
  • Oxidizing agents: Contamination with cleaning solutions or antiseptics
  • Prolonged specimen storage: WBC lysis over time releasing more esterase

False Negative Results

Conditions where pyuria may be present but leukocyte esterase is negative:

  • Early infection: Insufficient time for WBC accumulation in urine
  • Low WBC counts: Fewer than 10-15 WBCs/HPF may not trigger positive result
  • Glycosuria: High glucose levels can interfere with enzyme reaction
  • Proteinuria: Heavy protein concentration may inhibit esterase activity
  • High urine specific gravity: Concentrated urine may inhibit test reaction
  • Antibiotic treatment: Recent or current antibiotics reducing WBC response
  • Vitamin C (ascorbic acid): High concentrations can cause false negative
  • Tetracycline: Can cause false negative reaction
  • Boric acid preservatives: May interfere with enzyme activity

Collection and Testing Factors

  • Improper specimen collection: Use midstream clean-catch technique
  • Delayed testing: Test within 1-2 hours; refrigerate if delay unavoidable
  • Expired dipsticks: Use dipsticks before expiration date
  • Dipstick storage: Store in sealed container away from moisture
  • Reading time: Read results at specified time (usually 2 minutes)
Clinical Pearls
Clinical Pearl
"LE positive + nitrites positive = high probability UTI": The combination of positive leukocyte esterase and positive nitrites has approximately 95% specificity for bacterial urinary tract infection. This combination strongly supports empiric antibiotic treatment while awaiting culture results.
Clinical Pearl
LE positive without nitrites is common: Many UTIs will show positive leukocyte esterase with negative nitrites. This pattern is typical for non-E. coli infections (Staphylococcus saprophyticus, Enterococcus, Pseudomonas) that don't produce nitrate reductase. Don't rule out UTI based on negative nitrites alone.
Clinical Pearl
Sterile pyuria requires investigation: Positive leukocyte esterase with negative urine culture (sterile pyuria) suggests tuberculosis, fungal infection, interstitial nephritis, kidney stones, or recently treated infection. Consider TB culture, fungal culture, or imaging studies based on clinical context.
Microscopy confirms dipstick findings: Always confirm positive leukocyte esterase with microscopic urinalysis. Microscopy can identify WBC casts (suggesting pyelonephritis), bacteria, and rule out contamination. The dipstick is a screening tool, not a definitive diagnostic test.
Don't treat dipstick alone: Avoid diagnosing and treating UTI based solely on dipstick urinalysis without clinical symptoms. Asymptomatic bacteriuria is common in elderly patients, pregnant women, and catheterized patients and may not require treatment except in specific populations.
Negative LE has high negative predictive value: A negative leukocyte esterase test in a properly collected specimen makes UTI unlikely. The negative predictive value is approximately 95-98% when combined with negative nitrites. This can help avoid unnecessary antibiotic use.
Clinical Pearl
Collection technique matters: Improper collection is the most common cause of false positive results. Ensure midstream clean-catch technique to minimize vaginal or skin contamination. In difficult-to-collect populations, consider catheterized specimen or suprapubic aspiration.
Pregnancy considerations: Asymptomatic bacteriuria in pregnancy (positive culture without symptoms) requires treatment due to risk of pyelonephritis and adverse pregnancy outcomes. Screen all pregnant women with urinalysis and culture in first trimester and treat positive results.
Catheter-associated specimens: Positive leukocyte esterase is common in catheterized patients and may represent colonization rather than infection. Diagnose catheter-associated UTI based on symptoms (fever, suprapubic pain, costovertebral angle tenderness) plus positive urinalysis and culture.
References
  1. Kratz, A., Ferraro, M., Sluss, P. M., & Lewandrowski, K. B. (2004). Laboratory reference values. New England Journal of Medicine, 351, 1548-1564.
  2. Lee, M. (Ed.). (2009). Basic skills in interpreting laboratory data. Ashp.
  3. Farinde, A. (2021). Lab values, normal adult: Laboratory reference ranges in healthy adults. Medscape. https://emedicine.medscape.com/article/2172316-overview?form=fpf
  4. Nickson, C. (n.d.). Critical Care Compendium. Life in the Fast Lane • LITFL. https://litfl.com/ccc-critical-care-compendium/
  5. Farkas, Josh MD. (2015). Table of Contents - EMCrit Project. EMCrit Project. https://emcrit.org/ibcc/toc/
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