Metrological traceability of values for catalytic concentration of enzymes assigned to a calibration material

Background: The metrological traceability of values for the catalytic concentration of several enzymes assigned to a calibration material has been assured by following the recently published International Standard ISO 18153. Methods: A traceable value with a measurement uncertainty was assigned for the catalytic concentration of alanine aminotransferase, creatine kinase, γ-glutamyltransferase and lactate dehydrogenase in two materials from different sources. These are all measurable quantities, with the primary reference measurement procedure described by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and a primary calibrator giving metrological traceability to the SI unit of measurement. The metrologically traceable calibration was validated by measuring human serum samples using the primary reference measurement procedure and a routine commercial measurement procedure calibrated with the traceable materials. Results: Results showed that the primary reference procedure, selected manufacturers' procedures and the end-user's routine procedure for each enzyme have the same analytical specificity. Four of eight commercial calibrators tested were commutable, whereas the others had a very small difference in absolute terms, indicating that these materials would be useful for calibration. Conclusion: The implementation of a reference system for enzyme measurements was demonstrated that assures the traceability of patient results to SI units. © 2006 by Walter de Gruyter.