Is leukocyte (white blood cell) esterase the same as WBC (white blood cell) esterase?

Leukocyte Esterase and WBC Esterase Are the Same Test

Leukocyte esterase and WBC esterase are identical tests, as they both detect the same enzyme released from white blood cells in body fluids. 1

Understanding Leukocyte/WBC Esterase

Leukocyte esterase is an enzyme released specifically from white blood cells (leukocytes) that serves as a marker for inflammation or infection. This test is commonly used in urinalysis to detect the presence of white blood cells in urine, which may indicate a urinary tract infection (UTI).

Key characteristics of leukocyte esterase testing:

• Diagnostic accuracy: Leukocyte esterase has a sensitivity of 83% (67-94%) and specificity of 78% (64-92%) for detecting UTIs 1
• Source: The enzyme is released only from leukocytes (white blood cells) 2
• Detection method: Commonly measured using dipstick tests that change color in the presence of the enzyme 2

Clinical Applications

Leukocyte/WBC esterase testing is primarily used in:

1. Urinary tract infection diagnosis:

   • A positive leukocyte esterase test indicates pyuria (presence of WBCs in urine)
   • When combined with nitrite testing, sensitivity increases to 93% (90-100%) 1
   • Negative leukocyte esterase has excellent negative predictive value for ruling out UTI 1

2. Other body fluid testing:

   • Can be used to detect leukocytes in vaginal secretions 3
   • Has been explored as a potential biomarker for inflammatory bowel disease in fecal samples 4

Interpretation Considerations

When interpreting leukocyte esterase results, consider:

• Urine specific gravity: There is a weak but statistically significant negative correlation between specific gravity and leukocyte esterase pad performance (r = -0.12, p < 0.05) 5
• Collection method: Results may vary based on urine collection method (bag vs. catheterization) 6
• False positives: A positive leukocyte esterase result should be interpreted in clinical context, as it has limited positive predictive value 1

Common Pitfalls

• Relying solely on leukocyte esterase: While highly sensitive (100% in some studies), specificity can be lower (76%), leading to false positives 2
• Ignoring clinical context: UTI diagnosis should be primarily based on symptoms with urinalysis as supporting evidence 1
• Misinterpreting pyuria: Pyuria indicates inflammation but can be present in many non-infectious conditions 1
• Not obtaining cultures when indicated: Always obtain culture before starting antibiotics in complicated UTIs, recurrent infections, or treatment failures 1

In summary, leukocyte esterase and WBC esterase refer to the same diagnostic test that detects enzymes released from white blood cells. This test is widely used in clinical practice, particularly for screening urinary tract infections, with excellent sensitivity but moderate specificity.