Microscopic Examination of Urine - Chapter 7: Crystals

  • Purpose of QC on Chemical Reagent Strips: To ensure the accuracy and reliability of test results, minimizing errors caused by reagent degradation or storage issues.

  • Factors Leading to Errors on Chemical Strips:

    • Improper storage conditions (temperature and humidity).

    • Expired or degraded reagents.

    • Contamination of strips or urine samples.

    • User handling errors (incorrect timing or technique).

  • Chem Strip Analytes and Their Appropriate Chemical Methodology:

    • pH: Measured using pH indicators that change color based on acidity.

    • SG (Specific Gravity): Determined through a color change based on concentration.

    • Protein: Detected using protein indicators that react with protein molecules.

    • Ketones: Identified through nitroprusside reaction.

    • Glucose: Measured using glucose oxidase method.

    • Blood: Detected using peroxidase activity of hemoglobin.

    • Urobilinogen and Bilirubin: Measured using Ehrlich's reagent reaction.

    • Nitrites: Detected through a reaction with sulfanilamide.

    • Leukocyte Esterases: Detected through specific enzyme substrate reactions.

  • False Positive and False Negative Interfering Substances:

    • Protein: High concentrations of glucose or free hemoglobin can cause false positives.

    • Ketones: Ammonium sulfate can lead to false positives.

    • Glucose: Presence of ascorbic acid may lead to false negatives.

    • Blood: Certain medications can cause false positives.

    • Urobilinogen: Increased alcohol consumption can lead to falsely elevated results.

  • Confirmatory Tests for Carbohydrates:

    • Used to verify the results of initial screenings.

    • Why are confirmatory tests used for glucose?: To eliminate false positives and ensure accurate identification of glucose levels.

  • Reducing Sugars: Carbohydrates that can reduce other compounds, generally tested via Fehling's or Benedict's solution.

  • Ketones: Formed during fat metabolism, especially under starvation conditions or diabetes. These can lower the pH of urine.

  • Three Major Forms from Fat Metabolism: Acetoacetic acid, beta-hydroxybutyric acid, and acetone, with acetoacetic acid being present in the greatest amount.

  • Definition of Importance of Glucose and Galactose: Essential for energy production and cellular function.

  • Nitrites: Pathological indication of urinary tract infections, primarily caused by bacteria that convert nitrates to nitrites (e.g., E. coli).

    • False Negative Interferences: High concentrations of ascorbic acid, intake of antibiotics, or improper sample collection.

  • Leukocyte Esterases: Pathological indication of bacterial infections in the urinary tract.

    • Non-Bacterial: Conditions like interstitial cystitis can lead to false positives.

    • Time to Perform LE Test: Usually within 2 hours of sample collection for accuracy.

    • Positive and Negative Interfering Substances: Various urine substances may affect results, including medications.

  • Bilrubin: Refers to conjugated bilirubin, which is water-soluble.

    • Causes of Elevated Conjugated Bilirubin: Liver diseases, hemolytic conditions, or bile duct obstruction.

    • When CB is Elevated, Levels of Urobilinogen: Typically decrease due to interrupted flow.

  • Chemical Methods: Various reagents used to measure bilirubin and urobilinogen concentrations.

    • Positive and Negative Interfering Substances: Factors that can alter test results, including drugs or diet.

    • Confirmatory Test for Bilirubin: Often involves additional chemical testing beyond the initial strip test.

  • Urobilinogen: Elevated levels may indicate liver dysfunction.

    • When Urobilinogen is Elevated, Levels of CB: Generally decrease.

    • Chemical Methods: Including Erlich's method, used for concentration analysis.

    • Negative Interfering Substances: Factors impacting accuracy include certain medications or dietary influences.