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

Leukocytes in Urine: Clinical Significance and Management

Leukocytes in urine indicate inflammation in the urinary tract but do NOT automatically mean a UTI—treatment requires BOTH pyuria AND specific urinary symptoms (dysuria, frequency, urgency, fever, or gross hematuria). 1

Diagnostic Interpretation

The presence of leukocytes alone has critical limitations that must be understood:

• Leukocyte esterase testing has moderate sensitivity (83%) but limited specificity (78%) when used alone, meaning many false positives occur from non-infectious inflammation 1, 2

• When combined with nitrite testing, diagnostic accuracy improves dramatically to 93% sensitivity and 96% specificity, making this the most reliable dipstick combination 1, 3

• The absence of both leukocyte esterase AND nitrite has excellent negative predictive value (90.5%), effectively ruling out UTI in most populations 1

• Pyuria (≥10 WBCs/high-power field) is present in 15-50% of asymptomatic individuals, particularly in elderly and long-term care residents, representing colonization rather than infection 1

Critical Distinction: UTI vs. Asymptomatic Bacteriuria

The key distinguishing feature is the presence of symptoms—positive leukocytes without urinary symptoms represents asymptomatic bacteriuria, which should NOT be treated: 1, 3

• Do not treat pyuria alone, even with positive culture, in asymptomatic patients (Infectious Diseases Society of America Grade A-II recommendation) 1

• Treatment of asymptomatic bacteriuria causes more harm than good by promoting antibiotic resistance without clinical benefit 1, 3

• Non-specific symptoms like confusion or functional decline in elderly patients do NOT justify UTI treatment without specific urinary symptoms 1

When to Proceed with Treatment

Initiate evaluation and treatment ONLY when BOTH criteria are met: 1

1. Pyuria present (positive leukocyte esterase OR ≥10 WBCs/high-power field)
2. Acute onset of specific UTI symptoms:
   • Dysuria
   • Urinary frequency
   • Urinary urgency
   • Fever
   • Gross hematuria 1, 2

Mandatory Diagnostic Steps Before Treatment

Always obtain urine culture before starting antibiotics when treating symptomatic UTI: 3, 2

• Culture guides definitive antibiotic therapy and detects resistance patterns, which cannot be determined from urinalysis alone 3

• Ensure proper specimen collection: midstream clean-catch in cooperative adults, or in-and-out catheterization in women unable to provide clean specimens 1

• In febrile infants <2 years, always obtain both urinalysis AND culture before antibiotics, as 10-50% of culture-proven UTIs have false-negative urinalysis 4, 1, 3

Empiric Treatment Protocol (When Indicated)

When both pyuria and symptoms are present, start empiric antibiotics immediately after obtaining culture: 3, 2

• First-line treatment: Trimethoprim/sulfamethoxazole (160 mg TMP/800 mg SMX) every 12 hours for 3-5 days in uncomplicated UTI 2

• The high specificity (96%) of combined positive leukocyte esterase and nitrite justifies empiric treatment while awaiting culture results 3

• Re-evaluate based on clinical course and culture results to adjust therapy if needed 3

Special Population Considerations

Febrile infants and young children (<2 years): 4, 1, 3

• Obtain urine culture regardless of urinalysis results
• Young infants have particularly poor nitrite sensitivity due to frequent voiding and short bladder dwell time
• Nitrite requires approximately 4 hours of bladder dwell time to convert dietary nitrates

Elderly and long-term care residents: 1

• Evaluate ONLY with acute onset of specific urinary symptoms
• Do not screen for or treat asymptomatic bacteriuria (Infectious Diseases Society of America Grade A-I recommendation)
• Prevalence of asymptomatic bacteriuria is 15-50% in this population

Catheterized patients: 1, 3

• Do not screen for or treat asymptomatic bacteriuria
• Initiate antibiotics only if symptomatic (fever >38.3°C, hemodynamic instability, rigors)
• Change catheter before collecting culture specimen

Common Pitfalls to Avoid

• Never treat based on urinalysis alone without symptoms—this leads to unnecessary antibiotic exposure and resistance 1

• Bagged urine specimens in infants have 85% false-positive rates—always confirm with catheterized specimen before treating 3

• Do not interpret cloudy or smelly urine as infection in elderly patients—these observations alone do not indicate symptomatic infection 1

• In patients with suspected pyelonephritis or urosepsis, proceed with culture despite negative leukocyte esterase if systemic signs are present 1