Chemical Examination of Urine Part IV: Nitrite & Leukocyte Esterase Ricki Otten MT(ASCP)SC

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: 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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