What does the presence of leukocytes (white blood cells) in urine indicate and how is it treated?

Leukocytes in Urine: Clinical Significance and Management

What Leukocytes in Urine Indicate

Leukocytes in urine (pyuria) indicate inflammation in the genitourinary tract, but their presence alone does NOT diagnose infection and should never trigger treatment without accompanying urinary symptoms. 1

The clinical significance depends entirely on the presence or absence of symptoms:

In Symptomatic Patients

• When leukocytes appear with dysuria, frequency, urgency, fever, or gross hematuria, this strongly suggests a urinary tract infection (UTI). 1
• The combination of positive leukocyte esterase with positive nitrite achieves 96% specificity for UTI (combined sensitivity 93%). 1
• Leukocyte esterase testing alone has moderate sensitivity (83%) but limited specificity (78%), which improves dramatically when combined with nitrite testing. 1

In Asymptomatic Patients

• Asymptomatic bacteriuria with pyuria is extremely common (15-50% prevalence in long-term care residents) and should NEVER be treated. 1, 2
• The positive predictive value of pyuria alone for actual infection is exceedingly low because it reflects genitourinary inflammation from many noninfectious causes. 1
• In elderly patients, non-specific symptoms like confusion or functional decline alone should not trigger UTI evaluation or treatment without specific urinary symptoms. 1

Diagnostic Approach Algorithm

Step 1: Assess for Specific Urinary Symptoms

• If NO specific urinary symptoms are present (dysuria, frequency, urgency, fever, gross hematuria, new/worsening incontinence, suprapubic pain), do NOT order urinalysis or culture. 1, 2
• If specific urinary symptoms ARE present, proceed to Step 2. 1

Step 2: Obtain Proper Specimen Collection

• For women: perform in-and-out catheterization to avoid contamination. 1, 2
• For cooperative men: use midstream clean-catch or freshly applied clean condom catheter. 1, 2
• Process specimen within 1 hour at room temperature or 4 hours if refrigerated. 1

Step 3: Perform Complete Urinalysis

• Check leukocyte esterase, nitrite, and microscopic examination for WBCs. 1, 2
• If BOTH leukocyte esterase AND nitrite are negative, UTI is effectively ruled out in most populations (negative predictive value 82-91%). 1
• If either is positive with typical symptoms, proceed to Step 4. 1

Step 4: Culture Decision

• Obtain urine culture BEFORE starting antibiotics if: 1, 2

  • Pyuria ≥10 WBCs/high-power field OR positive leukocyte esterase OR positive nitrite on clean specimen 1
  • Suspected pyelonephritis (fever >38.3°C, flank pain, systemic signs) 1
  • Recurrent UTIs requiring targeted therapy 1
  • Febrile infants under 2 years (10-50% have false-negative urinalysis) 1

• Do NOT obtain culture if: 1

  • Patient is asymptomatic regardless of urinalysis findings 1
  • Both leukocyte esterase and nitrite are negative 1

Treatment Principles

Treatment is indicated ONLY when BOTH pyuria (≥10 WBCs/HPF or positive leukocyte esterase) AND acute onset of UTI-associated symptoms are present. 1

What TO Do:

• Collect culture before starting antibiotics in symptomatic patients with significant pyuria. 1
• In uncomplicated cystitis with typical symptoms and positive urinalysis, empiric treatment may begin after culture collection. 1
• Adjust antibiotic dosing based on creatinine clearance in patients with renal impairment. 2

What NOT To Do:

• Do NOT treat asymptomatic bacteriuria with pyuria—this is a strong recommendation from the Infectious Diseases Society of America. 1
• Do NOT interpret cloudy or smelly urine as infection in elderly patients without specific urinary symptoms. 1
• Do NOT screen for or treat asymptomatic bacteriuria in catheterized patients. 1
• Do NOT treat elderly patients with delirium, confusion, or falls alone without specific urinary symptoms or systemic signs (fever, hemodynamic instability). 1

Special Population Considerations

Pediatric Patients (2-24 months)

• Require BOTH urinalysis suggesting infection AND ≥50,000 CFU/mL on culture for diagnosis. 1, 2
• Always obtain both urinalysis and culture before antibiotics in febrile infants. 1
• Use catheterization or suprapubic aspiration for definitive diagnosis (bag-collected specimens have only 15% positive predictive value). 1

Long-Term Care/Elderly Patients

• Evaluate ONLY with acute onset of specific urinary symptoms. 1, 2
• Absence of pyuria can exclude bacteriuria, but presence has low predictive value due to high prevalence of asymptomatic bacteriuria. 1
• Perform CBC with differential within 12-24 hours of symptom onset. 2

Catheterized Patients

• Do NOT screen for or treat asymptomatic bacteriuria. 1
• Reserve testing for symptomatic patients with fever, hypotension, or specific urinary symptoms. 1

Common Pitfalls to Avoid

• False-positive leukocyte esterase: Can occur with contaminated specimens, certain oxidizing agents, and some medications. 1
• False-negative leukocyte esterase: May occur with high urinary glucose, high specific gravity, or certain antibiotics. 1
• Contaminated specimens: High epithelial cells indicate contamination; if repeat specimen still shows contamination with strong clinical suspicion, consider catheterization. 1
• Mixed bacterial flora with negative culture: Highly suggestive of contamination, not true infection. 1