Week 8: Chemical UA

1. Week 8: Chemical UA • Sensitivity and specificity • Test principles • Reagent strip tests • Back-up confirmatory tests • Interfering substances: false positives and negatives

2. Urine Chemistries

4. Test Performance • Sensitivity: minimum concentration • Specificity: discrimination • Interference factors

7. pH • Normal: 4 - 8 (mean 6) • Control blood pH • Principle: Methyl red and Bromthymol blue double indicator method • Report to nearest 0.5 pH unit • Help identify crystals

10. Protein • Normal: negative • Sensitive indicator of renal diseases • Glomerulonephritis • Pyelonephritis • Malignant hypertension • Preeclampsia • Severe exercise • Principle: Protein error of pH indicator • Tetrabromphenyl blue buffered at pH 3.2 • Watch for false positive in alkaline urine

12. Back-Ups for Protein • 3% sulfosalicylic acid (SSA) • 0 to 4+ depending on precipitation • Trichloroacetic (TCA) acid • Heat and acetic acid

13. Microalbuminuria • > 20 mg/L (30-300 mg/day) albumin in urine • Not detectable with reagent strip (6-15 mg/dL) or SSA (5 mg/dL) • Predictive of nephropathy and eventual renal failure in patients with type I diabetes mellitus • Detect patients with increased risk of renal and cardiovascular disease, associated with insulin resistance and endothelial dysfunction • Albumin to creatinine ratio corrects for hydration level

14. Glucose • Normal: negative • Blood threshold for glucose 175 mg% • Elevated with diabetes (hyperglycemia) • Principle: Glucose oxidase and hexokinase Glu Glu Ox > Gluconic acid + H2O2 H2O2 + o-tolidine Perosidase > color • Specific for glucose • Sensitive to redox agents

16. Back-Ups for Glucose • Lily TesTape • Specific to glucose • Clinitest (Benedict’s) • Non-specific for any • reducing agents • Cupper sulfate reduction • Cu++ (blue) + Glu ——> CuO (yellow-red)

17. Ketone Bodies • Normal: negative • Elevated with diabetic ketoacidosis, starvation • Most sensitive to acetoacetate, less sensitive to acetone, not sensitive to b-hydroxy butyrate • Principle: Sodium nitroprusside Legal’s test • Some have glycine to increase sensitivity to acetone

19. Back-Ups for Ketone • Acetest table test • Same principle as reagent strip • Gerhardt’s • FeCl3 non-specific test

20. Urobilinogen • Normal: up to 1 Ehrlich unit/dL (not negative) • Negative in complete obstruction of common bile duct • Elevated in liver disease and hemolytic anemia • Principle: p-dimethylaminobenzaldehyde, azocoupling in acid to form pink azo dye

23. Back-Up for Urobilinogen • Watson-Schwartz • Extraction with chloroform and butanol • Not commonly done

24. Bilirubin • Normal: negative • Liver disease • Viral hepatitis • Cirrhosis • Obstructive jaundice • Bile stone in common bile duct • Pancreatic cancer • Principle: Diazonium salt reaction, azo coupling in acid to form purple azo dye

26. Back-Ups for Bilirubin • Ictotest • Same principle as reagent strip • Harrison’s spot test • Fouchet’s reagent (TCA)

27. Blood • Normal: negative • Hematuria, hemoglobinuria, myoglobinuria • Principle: Hb used as catalyst for o-tolidine or benzidine oxidation (pseudo-peroxidase activity) • If hematuria, should see red cells • Menstrual contamination • Bacterial peroxidase can cause false positive

29. Nitrite • Some bacteria reduce nitrate to nitrite • Diazotization with aromatic amine like p-arsanilic acid or sulfanilamide

30. Leukocyte Esterase • Leukocyte (neutrophil) esterase cleave an ester which is azocoupled with aromatic amine • Correlate with microscopic WBC

31. Specific Gravity • Measure ionic solute • As protons are released from polyelectrolytes, pH decreases that change bromthymol blue indicator

32. Ascorbic Acid • Ascorbic acid reduces a dye causing color change • 2,6-dichlorophenolinedophenol

33. Quality Control and Quality Assurance

34. Homework • Construct a table tests: stix and back ups