From the Guidelines
Leukocyte esterase is a crucial marker in urinalysis for diagnosing Urinary Tract Infections (UTI), with a sensitivity of 88% and specificity of 79% when combined with nitrite testing, as reported in a Class II meta-analysis of diagnostic tests for UTI 1. The significance of leukocyte esterase in UTI diagnosis lies in its ability to detect enzymes released by neutrophils in the urine, indicating the presence of white blood cells and suggesting inflammation or infection in the urinary tract. When evaluating a patient with suspected UTI, a positive leukocyte esterase result should prompt consideration of empiric antibiotic therapy while awaiting urine culture results, as recommended by the Infectious Diseases Society of America 1. Key points to consider when interpreting leukocyte esterase results include:
- The test can yield false positives in cases of contamination or other inflammatory conditions
- False negatives can occur in patients with neutropenia or taking high doses of vitamin C
- Clinical correlation is essential, and the test should be interpreted alongside other urinalysis findings such as nitrites and microscopic examination for bacteria and white blood cells
- A minimum laboratory evaluation for suspected UTI should include urinalysis for determination of leukocyte esterase and nitrite level by use of a dipstick and a microscopic examination for WBCs, as recommended by the Infectious Diseases Society of America 1. In terms of treatment, common first-line options for uncomplicated UTI include nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin, with the specific choice depending on factors such as patient symptoms, medical history, and local antibiotic resistance patterns 1. It is also important to note that a positive leukocyte esterase result should prompt a urine culture obtained by catheterization or suprapubic aspiration, especially in cases where the urine specimen was obtained by bag, as the positive predictive value of a urinary culture obtained from a bag is only 15% 1.
From the Research
Significance of Leukocyte Esterase in Urinary Tract Infections
- Leukocyte esterase (LE) is a useful marker for diagnosing urinary tract infections (UTIs) 2, 3, 4, 5
- The presence of LE in urine indicates pyuria, which is a significant indicator of UTI 2, 3
- Studies have shown that LE tests have high sensitivity and specificity in detecting UTIs, making them a valuable screening tool 3, 5
- The sensitivity of LE tests ranges from 63.6% to 100%, while specificity ranges from 44.2% to 76% 2, 3, 5
Comparison with Other Diagnostic Methods
- LE tests have been compared to microscopic examination and urine culture, with results showing a significant correlation between LE tests and microscopic examination 2
- LE tests have also been compared to nitrite tests, with results showing that LE tests are more sensitive but less specific than nitrite tests 3, 5
- Urine culture is considered the gold standard for diagnosing UTIs, but LE tests can be used as a rapid and simple screening technique 3, 5
Clinical Applications
- LE tests can be used to detect UTIs in outpatient clinics and emergency departments 2, 3
- LE tests can also be used to monitor patients with recurrent UTIs or to detect UTIs in patients with indwelling urinary catheters 4
- However, some studies suggest that LE tests may not be necessary as a pre-operative screening test for gynaecological surgery, as asymptomatic bacteriuria is common in women and routine screening may lead to unnecessary intervention 6