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George G Klee, Assay Configuration and Analytic Specificity May Have Major Effects on Prediction of Clinical Outcomes— Implications for Reference Standards, Clinical Chemistry, Volume 55, Issue 5, 1 May 2009, Pages 848–849, https://doi.org/10.1373/clinchem.2009.124172
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In this month’s issue of Clinical Chemistry, Anborgh et al. demonstrate that differences in assay configuration can produce major differences in the association of plasma osteopontin measurements with survival in prostate cancer (1). Prediction of survival was found to be significantly better with assays that have a monoclonal antibody targeted to a specific epitope on the osteopontin molecule. This linkage between assay configuration and clinical utility may have major implications on the way reference materials and reference methods are formulated, because, as this report shows, the reference standards may need to focus on specific forms of the analyte.
Various national and international organizations are working to develop reference standards to help harmonize diagnostic assays. The European Union In Vitro Diagnostics Directive (98/79/EC) requires manufacturers marketing in the European Union to provide evidence that the values assigned to calibrators and control materials are traceable, through available reference measurement procedures and reference materials (when available), to standards of a higher metrological order (2)(3). The Joint Committee on Traceability in Laboratory Medicine (JCTLM)1 has helped guide the logistics of traceability with the use of European Committee for Standardization (CEN) and International Organization for Standardization (ISO) standards (4). ISO document 17511 distinguishes 2 broad categories of measurands: type A analytes, which are traceable to International System (SI) units, and type B analytes, which are not traceable to SI units (5). Type A analytes include a limited number of well-defined small molecules, such as electrolytes and steroid hormones, whereas type B analytes include most proteins and other laboratory measurements. Reference methods for type B analytes generally are less well developed, but JCTLM has a program for evaluating proposed methods.
