From the Guidelines
A positive Leukocyte Esterase (LE) test without Nitrite presence in a Urinalysis suggests inflammation in the urinary tract, but does not definitively confirm a bacterial urinary tract infection (UTI), and further evaluation, including urine culture, is recommended. This pattern can indicate an early or partial UTI, non-bacterial urethritis, or contamination of the sample. The presence of leukocyte esterase indicates white blood cells in the urine, reflecting inflammation, while nitrites are produced when certain bacteria convert urinary nitrates to nitrites. Some bacteria don't produce nitrites, explaining why this combination can still represent infection despite the negative nitrite result 1.
Key Considerations
- The specificity of urine dipstick tests ranges from 20% to 70% in the elderly, making it essential to interpret results in the context of clinical symptoms 1.
- Asymptomatic bacteriuria is common in older adults, and treatment should be reserved for those with symptoms of UTI, such as dysuria, frequency, urgency, and suprapubic pain 1.
- Empiric antibiotic therapy may be considered if symptoms are present, typically with nitrofurantoin 100mg twice daily for 5-7 days, trimethoprim-sulfamethoxazole DS twice daily for 3 days, or fosfomycin 3g single dose 1.
- Urine culture is recommended to identify potential pathogens and guide antibiotic therapy, especially in cases of suspected urosepsis or complicated UTI 1.
Clinical Approach
- In noncatheterized residents, diagnostic laboratory evaluation of suspected UTI should be reserved for those with acute onset of UTI-associated symptoms and signs 1.
- In residents with long-term indwelling urethral catheters, evaluation is indicated if there is suspected urosepsis, especially in the context of recent catheter obstruction or change 1.
- The minimum laboratory evaluation for suspected UTI should include urinalysis for determination of leukocyte esterase and nitrite level by use of a dipstick and a microscopic examination for WBCs 1.
From the Research
Significance of a Positive Leukocyte Esterase (LE) Test without Nitrite Presence
- A positive LE test without nitrite presence in a urinalysis may indicate a urinary tract infection (UTI) 2.
- The presence of LE activity is an indicator of pyuria, which is a sign of inflammation in the urinary tract 3, 4.
- A negative nitrite test with a positive LE test has been shown to have a high positive predictive value (79%) and sensitivity (82%) for UTI 2.
- However, a negative nitrite test with a positive LE test is not specific for UTI and may also be seen in other conditions such as contamination or inflammation 3, 5.
Diagnostic Accuracy
- The sensitivity of the LE test for detecting UTI has been reported to be around 63.6% to 66.7% 5.
- The specificity of the LE test for detecting UTI has been reported to be around 44.2% to 60.9% 5, 4.
- The presence of pyuria has been shown to have a higher sensitivity (95.6%) and specificity (60.9%) for positive urine culture compared to the LE test 5.
Clinical Implications
- A positive LE test without nitrite presence should be interpreted with caution and in the context of clinical symptoms and other diagnostic tests 3, 2.
- Empirical treatment for UTI should be based on clinical judgment and local antibiotic resistance patterns, rather than relying solely on urinalysis results 2, 6.
- Further evaluation, including urine culture and sensitivity testing, may be necessary to confirm the diagnosis and guide treatment 4, 6.