From the Guidelines
Leukocyte esterase is a more sensitive test than nitrate for detecting urinary tract infections, with a sensitivity of 83% compared to 53% for nitrite test, as reported in the 2011 Pediatrics study 1. When interpreting urine analysis results, it's crucial to consider the strengths and limitations of both esterase and nitrate tests.
- Leukocyte esterase test detects the presence of white blood cells in urine, indicating inflammation or infection, with a specificity of 78% 1.
- Nitrate test detects bacteria that convert urinary nitrates to nitrites, specifically indicating bacterial infection, particularly from gram-negative organisms, but with a lower sensitivity of 53% 1. The combination of both tests, leukocyte esterase or nitrite test positive, yields a high sensitivity of 93%, making it a useful screening tool for urinary tract infections 1. However, it's essential to consider the clinical context and interpret these results in conjunction with other urinalysis findings and patient symptoms, as false negatives can occur due to various factors, such as dilute urine or vitamin C ingestion 1.
- The performance characteristics of both leukocyte esterase and nitrite tests vary according to the definition used for positive urine culture results, the age and symptoms of the population being studied, and the method of urine collection 1. In real-life clinical practice, a positive leukocyte esterase test should be considered a strong indicator of urinary tract infection, especially when combined with a positive nitrite test, and further evaluation, such as urine culture, may be necessary to confirm the diagnosis 1.
From the Research
Esterase versus Nitrate on Urine Analysis
- The use of esterase and nitrate tests on urine analysis is a common practice for detecting urinary tract infections (UTIs) 2.
- However, the accuracy of these tests can be affected by various factors, such as the type of bacteria present, dietary habits, and urine dilution 3.
- A study found that a positive nitrite test is highly predictive of the absence of pure enterococcal bacteriuria, with a predictive value of 2.3% 4.
- Another study showed that the dipstick test for nitrite has low sensitivity, with 3-5% of urine samples suspected of UTI being nitrite-negative by dipstick test but positive for Enterobacterales in the urine culture 3.
- The leukocyte esterase test, on the other hand, can detect significant bacteriuria, but its accuracy can be affected by the presence of other substances in the urine, such as ascorbic acid 2.
- A study found that the absence of urinary nitrite should not affect routine empiric antibiotic choice for presumptive UTI in young children, as the prevalence of enterococcal UTI is low, at 3.2% 5.
Comparison of Esterase and Nitrate Tests
- The esterase test detects the presence of leukocyte esterase, an enzyme produced by white blood cells, while the nitrate test detects the presence of nitrate, a byproduct of bacterial metabolism 2.
- A study compared the two tests and found that a positive dipstick urinalysis (i.e., leukocyte esterase test and/or nitrite test) did not reliably detect significant bacteriuria in women with suspected uncomplicated UTI 2.
- Another study found that the dipstick test for nitrite is a safe alternative for investigating nitrite in urine samples, but its sensitivity can be affected by various factors, such as dietary habits and urine dilution 3.
Clinical Implications
- The results of esterase and nitrate tests should be interpreted with caution, taking into account the limitations and potential biases of each test 2, 3.
- Urine culture remains the gold standard for diagnosing UTIs, and empiric antibiotic treatment should be guided by local susceptibility patterns and clinical judgment 6, 5.
- Further studies are needed to evaluate the accuracy and clinical utility of esterase and nitrate tests in different patient populations and clinical settings 2, 3.