week 8 chemical ua
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Week 8: Chemical UA. Sensitivity and specificity Test principles Reagent strip tests Back-up confirmatory tests Interfering substances: false positives and negatives. Urine Chemistries. Test Performance. Sensitivity: minimum concentration Specificity: discrimination Interference factors.

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week 8 chemical ua
Week 8: Chemical UA
  • Sensitivity and specificity
  • Test principles
  • Reagent strip tests
  • Back-up confirmatory tests
  • Interfering substances: false positives and negatives
test performance
Test Performance
  • Sensitivity: minimum concentration
  • Specificity: discrimination
  • Interference factors
slide7
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
protein
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
back ups for protein
Back-Ups for Protein
  • 3% sulfosalicylic acid (SSA)
    • 0 to 4+ depending on precipitation
  • Trichloroacetic (TCA) acid
  • Heat and acetic acid
microalbuminuria
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
glucose
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
back ups for glucose
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)
ketone bodies
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
back ups for ketone
Back-Ups for Ketone
  • Acetest table test
    • Same principle as reagent strip
  • Gerhardt’s
    • FeCl3 non-specific test
urobilinogen
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
back up for urobilinogen
Back-Up for Urobilinogen
  • Watson-Schwartz
    • Extraction with chloroform and butanol
    • Not commonly done
bilirubin
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
back ups for bilirubin
Back-Ups for Bilirubin
  • Ictotest
    • Same principle as reagent strip
  • Harrison’s spot test
    • Fouchet’s reagent (TCA)
blood
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
nitrite
Nitrite
  • Some bacteria reduce nitrate to nitrite
  • Diazotization with aromatic amine like p-arsanilic acid or sulfanilamide
leukocyte esterase
Leukocyte Esterase
  • Leukocyte (neutrophil) esterase cleave an ester which is azocoupled with aromatic amine
  • Correlate with microscopic WBC
specific gravity
Specific Gravity
  • Measure ionic solute
  • As protons are released from polyelectrolytes, pH decreases that change bromthymol blue indicator
ascorbic acid
Ascorbic Acid
  • Ascorbic acid reduces a dye causing color change
  • 2,6-dichlorophenolinedophenol
homework
Homework
  • Construct a table tests: stix and back ups
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