What is the significance of a mildly positive Leukocyte (White Blood Cell) esterase result with otherwise normal urinalysis findings?

From the Guidelines

A mildly positive leukocyte esterase with otherwise negative urinalysis findings suggests the possible presence of white blood cells in the urine, which may indicate early or mild urinary tract inflammation or infection, and warrants clinical correlation with any symptoms the patient may be experiencing, such as urinary frequency, urgency, or discomfort. This result should be interpreted cautiously in the clinical context, considering the potential for false positives due to contaminated samples, highly concentrated urine, or certain medications 1.

Clinical Considerations

• If the patient is asymptomatic, watchful waiting with increased fluid intake and a repeat urinalysis in 1-2 weeks may be appropriate.
• If symptoms of urinary tract infection are present, empiric antibiotic treatment could be considered, typically with nitrofurantoin 100mg twice daily for 5 days, trimethoprim-sulfamethoxazole DS twice daily for 3 days, or fosfomycin 3g single dose.
• A urine culture should be obtained before starting antibiotics to confirm infection and guide therapy.

Diagnostic Approach

• The leukocyte esterase test detects enzymes released by white blood cells, and its sensitivity and specificity can vary depending on the population and testing method 1.
• The presence of pyuria or a positive dipstick test for leukocyte esterase is not highly predictive of bacteriuria, but the absence of pyuria can exclude bacteriuria 1.
• In patients suspected of urosepsis, urine and paired blood specimens should be obtained for culture and antimicrobial susceptibility testing, and a Gram stain of uncentrifuged urine should be requested 1.

Management

• The management of urinary tract infections in older adults or those with comorbidities may require a more tailored approach, considering the potential for asymptomatic bacteriuria and the need for careful antibiotic selection 1.
• In residents with long-term indwelling urethral catheters, evaluation is indicated if there is suspected urosepsis, and catheters should be changed prior to specimen collection and institution of antibiotic therapy 1.

From the Research

Leukocyte Esterase Test Results

• A mildly positive leukocyte esterase test result with all other items on urinalysis negative may indicate a urinary tract infection (UTI) 2, 3.
• The sensitivity of the leukocyte esterase test is around 63.6% to 66.7%, which means that it may not detect all cases of UTI 2.
• The presence of pyuria (white blood cells in the urine) is a more sensitive indicator of UTI, with a sensitivity of 95.6% 2.
• A study found that children with positive leukocyte esterase tests without pyuria were mostly prepubertal girls with a high rate of vulvovaginitis, which may lead to false positive results 3.

Clinical Implications

• The leukocyte esterase test can be used as a diagnostic tool for UTI, but it should be interpreted in conjunction with other clinical findings and laboratory results 2, 4.
• A positive leukocyte esterase test result may indicate the need for further testing, such as urine culture, to confirm the diagnosis of UTI 4, 5.
• The treatment of UTI typically involves antibiotics, such as nitrofurantoin, which has been shown to be effective in resolving UTI symptoms and eradicating the infection 4, 6.

Diagnostic Methods

• Microfluidic paper-based devices have been developed for the quantitative detection of leukocyte esterase in urine, which may provide a more accurate and sensitive method for diagnosing UTI 5.
• The use of these devices may help to reduce the number of false positive results and improve the diagnosis and treatment of UTI 5.