From the Guidelines
A urine sample can be colonized to yield a urinalysis result positive for nitrite and leukocyte esterase, indicating a potential urinary tract infection (UTI). This is because the nitrite test detects the presence of bacteria that convert nitrates to nitrites, such as gram-negative enteric bacteria, while the leukocyte esterase test detects white blood cells in the urine, reflecting an inflammatory response to infection 1.
Key Points to Consider
- The presence of either nitrite or leukocyte esterase has a sensitivity of 88% and a false positive rate of 7% for UTI 1.
- If both tests are positive, the specificity is 96%, indicating a high likelihood of UTI 1.
- Urine clarity can also be used to identify infected urine specimens, with clear urine having a negative predictive value of 97% 1.
Clinical Implications
- A positive result for both nitrite and leukocyte esterase should prompt empiric antibiotic therapy while awaiting urine culture results.
- Common first-line treatments include nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin, with amoxicillin-clavulanate or cephalexin being safer options for pregnant women.
- Patients should increase fluid intake and complete the full antibiotic course even if symptoms improve.
Evidence-Based Recommendation
Empiric antibiotic therapy is recommended for patients with a urinalysis positive for both nitrite and leukocyte esterase, while awaiting urine culture results. This approach is supported by the high specificity of the combined test results for UTI, as well as the potential for rapid progression of untreated UTIs to more severe infections 1.
From the Research
Urine Sample Colonization
- A urine sample can be colonized to yield a urinalysis result positive for nitrite and leukocyte (white blood cell) esterase, as these tests are indicators of bacteriuria and pyuria, respectively 2, 3, 4, 5, 6.
Conditions for Positive Results
- The presence of leukocyte esterase and nitrite in a urine sample can indicate a urinary tract infection (UTI), but these tests are not specific indicators of UTI and can have high false-negative rates 2, 3, 4.
- Pyuria, or the presence of white blood cells in the urine, is a better determinant of bacteriuria requiring therapy, and values significant for infection differ depending on the method of analysis 3.
Urinalysis Findings and Responsible Pathogens
- The relationship between urinalysis findings and responsible pathogens in children with UTIs has been studied, and it was found that E. coli more commonly causes leukocyturia, leukocyte esterase positivity, and pyuria, while pyuria might be lacking in UTIs associated with Klebsiella spp. and Enterococcus spp. 5.