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Chemical Examination of Urine Part IV: Nitrite & Leukocyte Esterase

Chemical Examination of Urine Part IV: Nitrite & Leukocyte Esterase. Ricki Otten MT(ASCP)SC uotten@unmc.edu. Nitrite: Purpose. Bacteria that contain a specific enzyme can reduce dietary nitrates to nitrites Rapid screening test for UTI. Nitrite: Normal. Normal: negative Abnormal:

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Chemical Examination of Urine Part IV: Nitrite & Leukocyte Esterase

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  1. Chemical Examination of UrinePart IV:Nitrite & Leukocyte Esterase Ricki Otten MT(ASCP)SC uotten@unmc.edu

  2. Nitrite: Purpose • Bacteria that contain a specific enzyme can reduce dietary nitrates to nitrites • Rapid screening test for UTI

  3. Nitrite: Normal • Normal: negative • Abnormal: • Cystitis: bladder • Pyelonephritis: kidney

  4. Nitrite: Method • Reagent strip test Nitrite + aromatic amine  diazonium salt Diazonium salt + aromatic compound  pink color • Sensitivity: 0.06-0.1 mg/dl nitrite ~ 10,000 organisms

  5. Nitrite: Method • Reagent strip test Specificity: • False positive: improper specimen handling; color masking • False negative: bacteria cannot reduce nitrates Bladder time not sufficient: need 4 hours Low nitrite levels Ascorbic acid Antibiotic inhibition of bacteria Further reduction of nitrites to nitrogen

  6. Leukocyte Esterase: Purpose • Increased WBC in urine is pathologic • Indicates inflammation, infection • Neutrophils most common type of WBC found in urine • Can detect intact WBC and lysed WBC

  7. Leukocyte Esterase: Normal • Normal: negative • Abnormal: • Bacterial infection: cystitis, pyelonephritis, urethritis • Non-bacterial infection: yeast, trichomonas

  8. Leukocyte Esterase: Method • Reagent strip: Granules in cytoplasm of WBC contain an enzyme (esterase) Ester –esterase aromatic compound Aromatic compound + diazonium salt  Purple colored complex

  9. Leukocyte Esterase • Sensitivity: 5-15 WBC/hpf • Specificity: • False positive: vaginal contamination; color masking • False negative: strong oxidizing agents (bleach); lymphocytes (no granules)

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