Lab Test: Leukocyte Esterase (Urine) Level
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An
indirect measure using a reagent strip to detect leukocyte esterase in urine to
assess for pyuria and/or presence of UTI
- Suspected gonococcal infection
- A positive leukocyte esterase test indicates the presence of nonspecific inflammatory enzymes and not necessarily Neisseria gonorrhoeae.
- Suspected pyuria in individuals at risk for urinary tract infection (UTI)
- Leukocyte esterase examination is a reasonable screening test for pyuria in patients with suspected UTI, but doe not directly measure bacteriuria. A negative test cannot exclude UTI in patients in whom signs and symptoms of UTI are ambiguous. A color change indicates that the enzyme is present; the intensity of the color is proportional to the amount of enzyme present.
- Vaginal fluids or Trichmonas can produce false positive results when present as contaminants in urine samples. Oxidizing agents and formalin can also produce false-positive results. The presence of nitrofurantoin and other chromogenic compounds can make color interpretation of the dipstick difficult.
- In children leukocyte esterase can be used for initial assessment of suspected UTI, but may not be reliable in children less than 2 years of age.
- Reliance on single parameters of the combined reagent strip may lead to treatment errors, in high risk groups (pregnancy, hospitalized patients), additional testing, including urine culture, should be considered.
- Urine culture and sensitivity - if urinalysis indicates the possibility of infection, a culture and sensitivity test should be performed.
- Nitrite (Urine) Lab Test
- False-positive results may occur in specimens contaminated by vaginal secretions (e.g., heavy menstrual discharge, Trichmonas infection, parasites) that contain WBCs.
- False-negative results may occur in specimens containing high levels of ascorbic acid.
- Results decreased in: elevated urine specific gravity, protein, or glucose
- Collect a fresh urine specimen in a sterile, urine container by clean-catch midstream voided specimen or catheterization.
- If the urine specimen contains vaginal discharge or bleeding, a clean-catch or midstream specimen will be needed. This requires meticulous cleaning of the urinary meatus with an antiseptic preparation to reduce contamination of the specimen by external organisms. The cleansing agent must then be completely removed so as not to contaminate the specimen.
- The midstream collection is obtained as follows:
- Have the patient begin to urinate into a bedpan, urinal, or toilet, then stop urinating. This washed urine out of the distal part of the urethra.
- Correctly position a sterile urine container and have the patient void 3 to 4 ounces of urine.
- Cap the container.
- Allow the patient to finish voiding.
- Measure with the dipstick method and the results will be determined by comparison with a color chart. A shade of purple is considered a positive result.
- Transport the urine specimen to the laboratory promptly.
- If the specimen cannot be processed immediately, refrigerate it. If the urine cannot be tested within 2 hours, a preservative may be required.
- Specimens can be initially screened with the dipstick and then cultured (gold standard for detecting bacteriuria), if properly obtained.
- Carroll KC et al. Laboratory evaluation of urinary tract infections in an ambulatory clinic. Am J Clin Pathol 1994;101:100-3.
- Stamm WE et al. New Engl J Med 1993;329:1328-34.
- White LV et al. Ann Intern Med 1993;118:230.
- LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests. First ed. Montvale, NJ: Thomson PDR; 2007.
- Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed. St. Louis, Missouri. 2014.
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Clinical Application
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