From the Guidelines
A positive leukocyte esterase result does not necessarily indicate contamination, but rather suggests the presence of white blood cells in the sample, typically indicating inflammation or infection. This test detects an enzyme produced by white blood cells and is commonly used in urinalysis to screen for urinary tract infections. When positive, it means neutrophils (a type of white blood cell) are present in the specimen, which often occurs in response to bacterial infection 1. Contamination would be indicated by other findings such as the presence of epithelial cells or multiple bacterial species in a urine culture.
Key Points to Consider
- The leukocyte esterase test should be interpreted alongside other clinical findings and tests like nitrite results, microscopic examination, and bacterial cultures to determine the true cause of the white blood cell presence.
- False positives can occur with certain medications, high vitamin C intake, or highly concentrated urine, so clinical correlation is always necessary.
- Studies have shown that the rate of contamination in urine samples can be reduced by proper collection methods, such as cleansing the perineum with soap before collecting the sample 1.
- The overall prevalence of UTI in febrile infants who have no source for their fever evident on the basis of history or physical examination results is approximately 5% 1.
Clinical Implications
- A positive leukocyte esterase result should prompt further evaluation, including urine culture and sensitivity testing, to confirm the diagnosis of a urinary tract infection.
- Clinicians should consider the clinical context and other laboratory results when interpreting a positive leukocyte esterase result, rather than assuming contamination.
- Proper urine collection and handling techniques can help minimize contamination and ensure accurate test results 1.
From the Research
Positive Leukocyte Esterase and Contamination
- A positive leukocyte esterase result does not necessarily indicate contamination, but rather the presence of white blood cells in the urine, which can be a sign of a urinary tract infection (UTI) 2, 3, 4, 5.
- However, a positive leukocyte esterase test can also be false positive, especially in prepubertal girls with vulvovaginitis or in boys with phimosis 6.
- The presence of pyuria (white blood cells in the urine) is an important factor in determining the likelihood of a UTI, and a positive leukocyte esterase test should be interpreted in conjunction with other clinical and laboratory findings, such as symptoms, physical examination, and urine culture results 3, 4, 5, 6.
- A study found that children with positive leukocyte esterase tests without pyuria were mostly prepubertal girls with a high rate of vulvovaginitis, and that unnecessary tests and treatments for UTI may be avoided with detailed history and physical examination in these cases 6.
- Another study found that the combination of pyuria and a positive urine culture confirmed UTI in 51% of patients, highlighting the importance of considering multiple factors when diagnosing UTI 5.