Leukocyte Esterase. This test measures esterase enzyme found in urinary leukocytes and enzyme released in poorly preserved specimens. If used alone diagnostically, this test is most beneficial for its high negative predictive value, especially with bacterial colony counts ≥ 105 cfu/mL. If one combines nitrite and leukocytes esterase testing of a clean-catch uncontaminated voided specimen,
the specificity of positive tests approaches 100 percent with uropathogen colony counts ≥ 105 cfu/mL. The negative predictive value is comparable. However, if these specimen have been contaminated with vaginal or colonic bacteria, this test can be falsely positive in the absence of a true uropathogen. Trichomonas species also species also produce esterases. In addition, very concentrated urine or urine with significant proteinuria or glucosuria will decrease the accuracy of this test.
Leukocyte Esterase. This test measures esterase enzyme found in urinary leukocytes and enzyme released in poorly preserved specimens. If used alone diagnostically, this test is most beneficial for its high negative predictive value, especially with bacterial colony counts ≥ 105 cfu/mL. If one combines nitrite and leukocytes esterase testing of a clean-catch uncontaminated voided specimen, the specificity of positive tests approaches 100 percent with uropathogen colony counts ≥ 105 cfu/mL. The negative predictive value is comparable. However, if these specimen have been contaminated with vaginal or colonic bacteria, this test can be falsely positive in the absence of a true uropathogen. Trichomonas species also species also produce esterases. In addition, very concentrated urine or urine with significant proteinuria or glucosuria will decrease the accuracy of this test.
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