From the Guidelines
Nitrite is more specific for urinary tract infections (UTIs) than leukocyte esterase, with a specificity of 98% compared to 78% for leukocyte esterase. When considering the diagnosis of UTIs, the specificity of the test is crucial to minimize false positives and unnecessary treatments. According to the study published in Pediatrics in 2011 1, the specificity of nitrite test is significantly higher than that of leukocyte esterase test. The nitrite test has a specificity of 98% (90-100%), making it a reliable indicator of bacterial infection, particularly gram-negative organisms like E. coli.
Some key points to consider when interpreting these results include:
- 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.
- The conversion of dietary nitrates to nitrites by bacteria requires approximately 4 hours in the bladder, which may affect the sensitivity of the nitrite test 1.
- Leukocyte esterase, while sensitive for detecting white blood cells in urine, is less specific for UTIs because white blood cells can be present in urine due to other conditions like vaginal contamination, kidney stones, or interstitial cystitis.
In clinical practice, using both tests together can provide optimal diagnostic accuracy, with nitrite providing higher specificity and leukocyte esterase offering better sensitivity 1. A positive result for both substantially increases the likelihood of a UTI. However, when considering specificity alone, nitrite is the more specific test for UTIs.
From the Research
Comparison of Leukocyte Esterase and Nitrite for UTI Diagnosis
- The sensitivity and specificity of leukocyte esterase and nitrite tests for diagnosing urinary tract infections (UTIs) have been evaluated in several studies 2, 3, 4, 5, 6.
- A study published in 2013 found that the sensitivity of leukocyte esterase test was 63.6%, while the combined leukocyte esterase and nitrite test had a sensitivity of 66.7% 2.
- Another study published in 2015 reported that the sensitivity and specificity of nitrite and leukocyte esterase tests were 75.74% and 68.90%, respectively 3.
- A 2018 study suggested that nitrites are likely more sensitive and specific than other dipstick components for UTI, particularly in the elderly 4.
- A 2014 study found that positive leukocyte esterase had a likelihood ratio of 2.5, and positive nitrites had a likelihood ratio of 2.8 in predicting E. coli versus non-E. coli infections 5.
- A 2004 study reported that the sensitivity rate for nitrite and leukocyte esterase testing was 0.64, and the specificity rate was only 0.52 in individuals with spinal cord injury 6.
Specificity of Leukocyte Esterase and Nitrite for UTI Diagnosis
- The specificity of leukocyte esterase and nitrite tests for UTI diagnosis varies across studies.
- A study published in 2013 found that the presence of pyuria had a higher specificity (60.9%) compared to the dipstick test (44.2%) 2.
- Another study published in 2015 reported that the specificity of nitrite and leukocyte esterase tests was 68.90% 3.
- A 2018 study suggested that nitrites are likely more specific than other dipstick components for UTI, particularly in the elderly 4.
- A 2004 study reported that the specificity rate for nitrite and leukocyte esterase testing was only 0.52 in individuals with spinal cord injury 6.