What does the presence of leukocytes (white blood cells) in the urine indicate?

Leukocyte Esterase in Urine: Clinical Significance

Leukocyte esterase in the urine indicates the presence of white blood cells (pyuria), which suggests inflammation in the urinary tract—but this finding alone does NOT diagnose a urinary tract infection and should never be treated without accompanying urinary symptoms. 1

What Leukocyte Esterase Actually Detects

• Leukocyte esterase is an enzyme released from white blood cells, detected through a dipstick chemical reaction that produces a color change (reported as negative, trace, 1+, 2+, or 3+). 1
• The test has moderate sensitivity (83%) but limited specificity (78%) for detecting UTIs, meaning many positive results occur without true infection. 1
• When combined with nitrite testing, diagnostic accuracy improves substantially to 93% sensitivity and 96% specificity. 1

Clinical Interpretation: When It Matters

Positive Leukocyte Esterase WITH Symptoms

• If the patient has specific urinary symptoms (dysuria, frequency, urgency, fever, or gross hematuria), a positive leukocyte esterase strongly suggests UTI and warrants treatment. 1
• In symptomatic patients, obtain a properly collected urine specimen for culture before starting antibiotics, especially in complicated cases. 1
• For uncomplicated cystitis in healthy nonpregnant women with typical symptoms, treatment can proceed without culture if both leukocyte esterase and nitrite are positive. 1

Positive Leukocyte Esterase WITHOUT Symptoms

• Asymptomatic bacteriuria with pyuria is extremely common (10-50% prevalence in elderly and long-term care residents) and should NOT be treated. 1, 2
• The Infectious Diseases Society of America provides Grade A-I evidence that treating asymptomatic bacteriuria leads to unnecessary antibiotic exposure, increased resistance, and no clinical benefit. 2
• Do not order urinalysis or urine cultures in asymptomatic individuals, even with non-specific symptoms like confusion or functional decline alone. 1

Negative Leukocyte Esterase

• A negative leukocyte esterase test has excellent negative predictive value (82-91%) and effectively rules out UTI in most populations. 1
• When both leukocyte esterase and nitrite are negative, UTI is essentially excluded with 90.5% negative predictive value. 1
• The absence of pyuria distinguishes asymptomatic bacteriuria (colonization) from true infection. 1

Diagnostic Algorithm

Step 1: Assess for Specific Urinary Symptoms 1

• Look for: dysuria, frequency, urgency, fever >38.3°C, gross hematuria, new/worsening urinary incontinence
• Non-specific symptoms (confusion, falls, malaise) do NOT qualify as UTI symptoms in elderly patients

Step 2: If Symptomatic, Obtain Proper Specimen 1

• Women: midstream clean-catch or in-and-out catheterization if contamination suspected
• Men: midstream clean-catch or freshly applied clean condom catheter
• Process within 1 hour at room temperature or 4 hours if refrigerated

Step 3: Interpret Urinalysis Results 1

• Both leukocyte esterase and nitrite negative → UTI ruled out
• Either positive + typical symptoms → treat as UTI (culture optional in uncomplicated cases)
• Positive without symptoms → likely asymptomatic bacteriuria, do NOT treat

Step 4: Culture Indications 1

• Always culture in: suspected pyelonephritis, pregnancy, recurrent UTIs, febrile infants <2 years, immunocompromised patients
• Optional in: uncomplicated cystitis with typical symptoms and positive urinalysis

Special Population Considerations

Elderly and Long-Term Care Residents 1, 2

• Asymptomatic bacteriuria prevalence is 15-50% in non-catheterized residents
• Evaluate only with acute onset of specific urinary symptoms or suspected urosepsis (fever, hypotension, rigors)
• Prospective studies show untreated asymptomatic bacteriuria persists 1-2 years without increased morbidity or mortality

Catheterized Patients 2

• Do not screen for or treat catheter-associated asymptomatic bacteriuria (Grade A-I evidence)
• Bacteriuria and pyuria are nearly universal in chronic catheterization
• Treating CA-ASB promotes antimicrobial resistance (47% vs 26% in treated vs untreated groups) without reducing subsequent infections

Pediatric Patients 1

• Febrile infants 2-24 months require both urinalysis and culture before antibiotics
• Leukocyte esterase sensitivity is 94% in clinically suspected UTI
• Bag-collected specimens have only 15% positive predictive value; use catheterization or suprapubic aspiration for definitive diagnosis

Common Pitfalls to Avoid

• Never treat pyuria alone without urinary symptoms—this is the most common error leading to unnecessary antibiotic use. 1, 2
• Do not attribute confusion, functional decline, or cloudy/smelly urine to UTI without specific urinary symptoms in elderly patients. 1
• False-positive results occur with contaminated specimens, certain oxidizing agents, and some medications. 1
• False-negative results may occur with high urinary glucose, high specific gravity, or certain antibiotics. 1
• In infants who void frequently, shorter bladder dwell time may result in fewer detectable leukocytes, lowering sensitivity. 1

Key Takeaway

The presence of leukocyte esterase indicates urinary tract inflammation (pyuria), not infection. 1 Its primary clinical utility is ruling out UTI when negative, not diagnosing it when positive. 1 The diagnosis of UTI must always be based on clinical symptoms combined with urinalysis findings—never on laboratory results alone. 1