203 Unit 1.1

Sample Types for Chemistry Testing

  • Serum Samples: Red top tube, Gold/Tiger top tube

  • Plasma Samples: Lithium heparin

Factors Affecting Results

  • Chemistry analyzers use photometry to measure analyte concentration.

  • Interferences: Hemolysis, lipemia, icterus affect serum and plasma analysis.

Hemolysis

  • Caused by improper sample handling, freezing, or vigorous mixing.

  • Appear orange/red; interferes with testing results.

    • Hematology: Causes falsely low HCT, PCV, and RBC count; high MCH, MCHC.

    • Chemistry: Increases absorbance, falsely elevates potassium, AST, magnesium, etc.

    • Causes dilution effects in serum concentrations.

Lipemia

  • Caused by high-fat meals or altered lipid metabolism; appears milky white.

  • Hematology: Falsely elevated hemoglobin, total protein, platelet counts.

  • Chemistry: Increased absorbance, affects bilirubin and test results.

  • Prevention: Fasting 12 hours; can be centrifuged or diluted post-collection.

Icterus

  • Caused by increased bilirubin; appears yellow-brown.

  • Hematology: No effects.

  • Chemistry: Falsely low values in creatinine and total protein due to bilirubin interference.

Patient Preparation for Chemistry Analysis

  • Fasting to avoid lipemia.

  • Medication timing considerations.

Chemistry Analyzers

  • Results available in ~10 minutes; rely on photometry.

  • Photometry: Measure light absorption related to analyte concentration.

  • Types of assays: End Point (stable end) and Kinetic (must measure at a specific time).

Standards and Controls

  • Standards: Non-biological reference solutions for calibrating analyzers.

  • Controls: Quality control samples with known concentrations.

Analyzer Reagents

  • Dry reagent systems (slides, pads) or liquid systems (lyophilized reagents).

  • Most tests done as panels or profiles (e.g., pre-anesthetic, kidney, equine).