Calibration and Quality Control

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  • Calibration and Quality Control
    • Methodology
      • calibration concentration must be within range of assay
        • Pure calibrants - SI units
        • heterogenous analytes - IU/L
        • concentration curve used to determine the concentration of unknown reactants
          • multipoint calibration curve is read the same way as a straight line curve
          • bumpy line - line of best fit
      • Heterogenous analystes - mixtures of related molecules. different assays might have different fractions
    • Internal quality control
      • detect, reduce and correct deficiencies
      • types of assay errors: changes in bias & ageing or reagents,
        • modern instruments - errors are rare
      • IQC  materials: known conc of analyte. should produce same value everyday
        • stable, aqliquotes/ vials, covers normal and abnormal ranges
      • new batches: run in new sampe. determine mean and SD, plot levey-jennings chart, rejection laws
      • assessment : check results against correct value and look for tends
    • Traceable systems of measurement
      • Traceability is an unbroken chain of comparisons of measurement leading to a known reference value
        • - Primary       reference         - primary         calibrator           - secondary      reference methods
      • Atomic absorption spectroscopy - quantitative determination of chemical elements using the absorption of optical radiation
      • Thermal ioniszation mass spectrometry - highly sensitive isotope mass spectometry technique. Uses thermal ionization effect.
    • Practical Aspects
      • Reasons to re-calibration
      • validity of calibration
    • Levey- Jennings Chart
      • the distance from the mean is measured in SD
      • A msrk is made indicating how far away the actual result is from the mean
      • 1 3s - control rule (mean plus 3 above and below)
      • 1 2s - waning rule (mean plus 2 aboe and below)
      • R 4s - reject when 1 control measurement in a group exceeds the mean plus 2s and another exceeds 2 minus
      • 10 x - reject when 1 control measurement in a group exceeds the mean +2 and another -2
    • Point of care assay QC
      • Format of assays
      • Training of operators
    • External Quality Assessment
      • comparable results between labs
      • Distribution of samples unknown composittion to different labs - collate results - find best method
        • Lab Accreditation - in line with legislation and best practice
          • inspection every 2-3 years
    • Total quality management : planning, improvement, lab practices, control & assurance

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