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Vitamin D Standardization Program (VDSP) Commutability

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An essential task in developing a reference measurement system is establishing that the Standardized Reference Materials® (SRMs), and the materials used in accuracy-based performance testing/external quality assessment programs are commutable. Commutability is defined as the equivalence of mathematical relationships between results obtained using different measurement procedures for representative samples. Demonstration of commutability is necessary in that materials used in PT/EQA programs are prepared from pooled serum samples. As a result, it is essential to document that such samples function in different assays just the way a sample from an individual patient would, i.e., that they are commutable.

Importantly, in 2013 the VDSP completed a commutability study from which preliminary data analyses suggest that SRM 972a, as well as College of American Pathologists (CAP) and Vitamin D External Quality Assessment Scheme (DEQAS) materials, are commutable. We are currently working to publish those results.

A new and larger study, VDSP Vitamin D Commutability Study 2, to test the commutability of SRM 972a and CAP and DEQAS materials in a wide range of currently used assay platforms is underway.* The Federal Register announcementexternal link disclaimer was released April 2015. We plan to begin shipping smaples to the participating laboratories in March 2016. 

*Camara J, Hoofnagle A, Carter G, Sempos C. Take two: Gearing up for the next vitamin D commutability study. Clin Lab News. 2015 Feb1:8.external link disclaimer