Chemical Examination of Urine Part IV: Nitrite

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Chemical Examination of UrinePart IVNitrite
Leukocyte Esterase

• Ricki Otten MT(ASCP)SC
• uotten_at_unmc.edu

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Nitrite Purpose

• Bacteria that contain a specific enzyme can
  reduce dietary nitrates to nitrites
• Rapid screening test for UTI

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Nitrite Normal

• Normal negative
• Abnormal
• Cystitis bladder
• Pyelonephritis kidney

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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

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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

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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

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Leukocyte Esterase Normal

• Normal negative
• Abnormal
• Bacterial infection
• cystitis, pyelonephritis, urethritis
• Non-bacterial infection yeast, trichomonas

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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

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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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