What is the role of urine esterase in diagnosing Urinary Tract Infection (UTI)?

From the Guidelines

Urine esterase testing should be used as part of a urinalysis dipstick, alongside nitrite testing, to aid in the diagnosis of urinary tract infections (UTIs), with a positive result for both tests having a specificity of 96% for UTI diagnosis. This approach is supported by a meta-analysis that found the presence of either nitrite or leukocyte esterase on a urine dipstick to have a sensitivity of 88% and a false positive rate of 7% for UTI 1. The leukocyte esterase test, in particular, has higher sensitivity but lower specificity compared to the nitrite test, making it a useful screening tool for UTIs. However, it is essential to consider the clinical symptoms and not rely solely on the urinalysis results for diagnosis, as the positive predictive value of pyuria for diagnosing infection is low 1.

In clinical practice, a positive leukocyte esterase test in a patient with UTI symptoms often justifies empiric antibiotic treatment while awaiting culture results, particularly in uncomplicated cases. This approach balances prompt treatment with antimicrobial stewardship. Key considerations include:

• The sensitivity and specificity of urine esterase testing
• The importance of using urine esterase testing alongside nitrite testing
• The need to consider clinical symptoms in addition to urinalysis results
• The role of urine cultures in guiding targeted therapy, particularly in complicated or recurrent cases.

It is crucial to weigh the benefits of prompt treatment against the risks of antimicrobial resistance and to use urine esterase testing as part of a comprehensive diagnostic approach that includes clinical evaluation and, when necessary, urine culture 1.

From the Research

Urine Estrase for UTI

• Urinary tract infections (UTIs) are common bacterial infections that require optimal treatment based on diagnostic tests and antimicrobial susceptibility of uropathogens 2.
• The performance characteristics of diagnostic tests, such as the nitrite test and leucocyte-esterase (LE) test, are crucial in determining the presence of UTIs 2.
• A positive nitrite test or a negative nitrite test with a positive LE test can confirm UTI, while a negative nitrite test with a negative LE test does not rule out infection 2.
• The use of nitrofurantoin, a wide-spectrum antibiotic, is recommended as first-line therapy for uncomplicated lower urinary tract infection (UTI) due to its low frequency of utilization and high susceptibility in common UTI pathogens 3.
• However, the presence of mild or moderate reductions in estimated glomerular filtration rate does not justify avoidance of nitrofurantoin 4.
• Dipstick urinalysis, including nitrites and leucocyte-esterase, is a useful diagnostic tool, but results must be interpreted in the context of the patient's pretest probability based on symptoms and characteristics 5.
• Urine culture is the gold standard for detection of UTI, and asymptomatic bacteriuria should not be treated with antibiotics 5.
• First-line treatments for UTI include nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole, which have minimal collateral damage and resistance 5.

Diagnostic Tests

• The nitrite test has a high positive predictive value (96%) and specificity (94%) for UTIs 2.
• The leucocyte-esterase (LE) test can be used in combination with the nitrite test to confirm UTI 2.
• Dipstick urinalysis, including nitrites and leucocyte-esterase, is a useful diagnostic tool, but results must be interpreted in the context of the patient's pretest probability based on symptoms and characteristics 5.
• Microscopic urinalysis is comparable to dipstick urinalysis as a screening test 5.
• Bacteriuria is more specific and sensitive than pyuria for detecting UTI, even in older women and during pregnancy 5.

Treatment

• Nitrofurantoin is a recommended first-line therapy for uncomplicated lower urinary tract infection (UTI) due to its low frequency of utilization and high susceptibility in common UTI pathogens 3.
• Fosfomycin and trimethoprim-sulfamethoxazole are also recommended as first-line treatments for UTI, but resistance levels should be considered 5.
• Beta-lactams, nitrofurantoin, fosfomycin, and trimethoprim-sulfamethoxazole can be appropriate treatments for UTI in pregnancy 5.