Traceability of Results via Medical Reference Materials

World Accreditation Day 2015Technical Seminar

Dr ID SiriwardhanaSenior Lecturer in Pathology

Faculty of MedicineUniversity of Ruhuna

Galle

Overview

• What is metrological traceability?• Is it important to ensure traceability of

results?• Who is responsible?• What are reference materials and reference

methods?• Are there analytes without reference

materials?

Metrology

• Definition – science of measurement• Measurements are comparisons against

known standards

Metrological Traceability

• Metrological Traceability “ property of a measurement result whereby the result can be related to a stated reference, through a documented unbroken chain of calibrations (comparisons),each contributing to the measurement uncertainty.”

International Vocabulary of Basic and General Terms in Metrology (VIM)

Metrological Traceability

• Key Features– It is a property of a measurement result– The results are obtained through a series of

comparisons to a reference standard– All comparison steps documented– Measurement uncertainty (MU)stated for each

comparison step– Preferably results traceable to an SI unit

What is the significance of traceability?

• Link measurement results of a patient sample to a commonly accepted reference (certified reference material or reference measurement procedure)

• Renders measurement results comparable across different – methods and systems– locations– times

ISO 15189:2012

• Metrological traceability shall be to a reference material or reference procedure of higher metrological order available.”

• “documentation of calibration traceability to a higher order reference material or reference procedure may be provided by an examination system manufacturer.”

What are Reference Materials?

Primary Reference Materials

•Used with a primary reference measurement procedure •To produce primary calibrators

Primary Calibrators

•Used to calibrate secondary reference measurement procedure•To produce secondary calibrators

Secondary Calibrators

•Used in manufacturer’s method•To produce master calibrators

Traceability Chain for Serum Calcium

SRM 915b (NIST) Mass Fraction of CaCO3

•Gravimetry•SRM 3109a

SRM 3109aAqueous CaCO3

•ID-TIMS•SRM 909b

SRM 909b(human serum)

•Atomic absorption spectrometry•Master calibrator (Ca in mmo/L)

Do all analytes have primary and secondary Calibrators?

• No• Reason: most analytes are yet inadequately

defined for– Physico-chemical characteristics– Molecular weights

• Alternative: International conventional calibrators; Eg. hormones

• Produced by international conventional reference measurement procedures

Lowest Order Metrological Traceability

• No international reference measurement procedure or calibrator

• Only a manufacturer’s method and calibrators• Eg. Tumour markers like CA 19-9

Information about Reference Materials

• Joint Committee for Traceability in Laboratory Medicine (JCTLM)

• National Institute of science and Technology (NIST)• Institute for Reference Materials and Measurements

(IRMM)• WHO Expert Committee on Biological Standardization

(WHO-ECBS)• International Federation for Clinical Chemistry and

Laboratory Medicine (IFCC)• International Council for Standardization in Haematology

(ICSH)