What does a high level of leukocyte (white blood cell) esterase in urine indicate?

Elevated Leukocyte Esterase in Urine: Clinical Significance and Interpretation

A high level of leukocyte esterase in urine indicates the presence of white blood cells (pyuria), suggesting inflammation in the urinary tract that may be due to infection, but requires clinical correlation with symptoms and additional testing for definitive diagnosis. 1, 2

Diagnostic Significance

• Leukocyte esterase is an enzyme released from white blood cells that can be detected through dipstick testing, with results typically reported as negative, trace, 1+, 2+, or 3+ based on color intensity 2
• The test has moderate sensitivity (83%) but limited specificity (78%) for urinary tract infections (UTIs), making it insufficient as a standalone diagnostic test 1
• When leukocyte esterase is combined with a positive nitrite test, the specificity increases to 96% with a sensitivity of 93%, significantly improving diagnostic accuracy 2
• The absence of pyuria (negative leukocyte esterase and no microscopic WBCs) has excellent negative predictive value for ruling out UTI 2

Clinical Interpretation

• Positive leukocyte esterase requires further diagnostic evaluation with urine culture before initiating antimicrobial therapy, unless the patient has clear symptoms of UTI such as fever, dysuria, or suspected bacteremia 1
• In symptomatic patients (dysuria, frequency, urgency, fever, gross hematuria), positive leukocyte esterase strongly suggests UTI and warrants obtaining a urine culture before starting antibiotics 1, 2
• The minimum laboratory evaluation for suspected UTI should include urinalysis for leukocyte esterase, nitrite, and microscopic examination for WBCs 2
• In asymptomatic individuals, a positive leukocyte esterase test should not automatically trigger antimicrobial treatment 2

Special Population Considerations

Elderly Patients

• Asymptomatic bacteriuria with pyuria is common in older adults (15-50% prevalence in non-catheterized long-term care facility residents) 3, 2
• Non-specific symptoms like confusion or functional decline alone should not trigger UTI treatment without specific urinary symptoms in older adults 2
• In long-term care facilities, evaluation is indicated only with acute onset of UTI-associated symptoms 2

Pediatric Patients

• In febrile infants and young children, positive leukocyte esterase should prompt urine culture collection before initiating antimicrobial therapy 2
• The test has lower sensitivity in infants who void frequently due to shorter bladder dwell time resulting in fewer detectable leukocytes 2

Limitations and Considerations

• False-positive results can occur with contaminated specimens, certain oxidizing agents, and some medications 2
• False-negative results may occur with high urinary glucose, high specific gravity, or certain antibiotics 2
• Microscopic pyuria (>10 WBCs/high-power field of spun urine) or a positive dipstick test for leukocyte esterase are not highly predictive of bacteriuria, but the absence of pyuria can exclude bacteriuria with a negative predictive value approaching 100% 3
• In rare cases, significant bacteriuria may occur without pyuria in persons with neutropenia or, occasionally, with normal peripheral WBC count 3

Alternative Causes of Elevated Leukocyte Esterase

• Beyond UTIs, elevated leukocyte esterase may indicate:
  • Inflammation from non-infectious causes 2
  • Urethritis, including chlamydial and gonococcal infections 2
  • Kidney stones 2
  • Interstitial nephritis 2