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  1. International Scientific Workshop on the Standardization of Genome Amplification Techniques for the Safety Testing of Blood, Tissues and Organs With Regard to Blood Borne Pathogens SoGAT XVII Synthetic Standards – SI vs IU Adrian Bristow NIBSC UK INFORMAL CONSULTATION ON LABORATORY SUPPORT FOR INTERNATIONAL BIOLOGICAL STANDARDIZATION 24 to 25 May 2004, M.505 Session 3 Review of the WHO procedure for preparation, characterization and establishment of international biological reference materials Traceability and uncertainty in biological reference materials A. F. Bristow

  2. International Standards relating to the establishment of Reference Materials, including those of Biological Origin prEN ISO 17511 In vitro diagnostic medical devices – Measurement of quantities in samples of biological origin – Metrological traceability of values assigned to calibrators and control materials ISO 15194 In vitro diagnostic medical devices -- Measurement of quantities in samples of biological origin -- Description of reference materials (C) World Health Organization World Health Organization, Technical Report Series, No. 800, 1990 Annex 4 GUIDELINES FOR THE PREPARATION,CHARACTERIZATION AND ESTABLISHMENT OF INTERNATIONAL AND OTHER STANDARDSAND REFERENCE REAGENTS FOR BIOLOGICAL SUBSTANCES(Revised 1989)

  3. prEN ISO 17511 WHO Single, defined Method SI units • 1 Cases with primary reference measurement procedure and primary • calibrator(s) giving traceability to SI units • Cases with International conventional reference measurement procedure (which is not primary) and international conventional calibrators without traceability to SI • Cases with International conventional reference measurement procedure (which is not primary) but no international conventional calibrators and without traceability to SI • Cases with International conventional calibrator (which is not primary) but no international conventional reference measurement procedure and without traceability to SI • Cases with manufacturer’s selected measurement procedure but neither International conventional reference measurement procedure nor international conventional calibrator and without traceability to SI • WHO guidelines produce standards: • calibrated in a multi-method study (rather than a single, reference method) • With values assigned in International units (rather than mg/mol) • 3 With no imprecision assigned to the ampoule content No defined methods arbitrary units

  4. From Saldanha et al: Collaborative study to calibrate hepatitis C Genotypes 2-6….. Vox Sanguinis (2003) 84 20-27 • Collaborative study (multi-method) • Unitage (IU) • Value assignment (arbitrary, no • uncertainty) • Traceability • All consistent with WHO paradigm • Can synthetic DNA standards, characterised in molecular terms, allow us to move • Away from the WHO paradigm, towards the top end of the 17511 hierarchy? • Is there a metrological argument? • Is there a biological argument

  5. ISO 15194 Checklist Title Page (Formatting) Forward (Formatting) Safety Precautions Clarity, instructions Scope Clarity Justification for choice Meets Intended Use of Material Characteristics Clarity, Unusual instructions/needs, commutability Validation Commutability Harmonizes Results Value assignment process Uncertainty, reproducibility Material Characteristics Uncertainty, consistency Intended Use Clarity Instructions for use Clarity Supplier Contact information After R. Miller, (2004) Commutability is considered an intrinsic property of the reference material

  6. Commutability Heinz Schimmel, IRMM Degree to which a material yields the same numerical relationships between results of measurements by a given set of measurement procedures, purporting to measure the same quantity, as those between the expectations of the relationships for the same procedures applied to those types of material for which the procedures are intended In other words: The ratio between the results of two procedures must be the same for the calibrator as for the routine samples A commutable calibrator is showing a similar behaviour to routine samples when different measurement procedures are applied Commutability is related to the corresponding measurement procedures and calibrator combinations but is not automatically valid for other combinations

  7. What is a “primary reference measurement procedure ? • 1 Cases with primary reference measurement procedure and primary • calibrator(s) giving traceability to SI units • Cases with International conventional reference measurement procedure (which is not primary) and international conventional calibrators without traceability to SI • Cases with International conventional reference measurement procedure (which is not primary) but no international conventional calibrators and without traceability to SI • Cases with International conventional calibrator (which is not primary) but no international conventional reference measurement procedure and without traceability to SI • Cases with manufacturer’s selected measurement procedure but neither International conventional reference measurement procedure nor international conventional calibrator and without traceability to SI ISO 17511 …having the highest metrological qualities, whose operation can be completely described and understood, for which a Complete uncertainty statement can be written down in Terms of SI units, and where results are therefore accepted Without reference to a measurement standard of the quantity Being examined Clinical Chemistry A reference method is generally accepted as being One where the analyte can be defined and measured In the sample to be tested (eg plasma). This gives you the Highest level of commutability

  8. The biological argument The SI unit might promote an inference of function from structure Mol phosphate Genome equivalent Virus number Infectivity “Not all RNA molecules are found in viruses. Not all RNA molecules found in viruses are full length and therefore infectious. Not all viruses containing full length RNA molecules are infectious”. P. Minor 2003