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Vitamin D Standardization Program (VDSP) Reference Measurement System

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VDSP Reference Measurement System (RMS) Specifics

VDSP developed an RMS to establish the world-wide standardization of 25-hydroxyvitamin D [25(OH)D] measurements.

  • National Institute of Standards and Technology (NIST) and Ghent University Reference Measurement Procedures (RMPs).
    RMPs are the "gold-standard" laboratory procedures for measuring 25(OH)D; that is, the concentration values obtained using the NIST or the Ghent RMPs are considered to be the true concentrations. [Joint Committee for Traceability in Laboratory Medicine database: Laboratory medicine and in-vitro diagnostics.external link disclaimer]
  • NIST Standard Reference Materials® (SRMs).
    http://www.nist.gov/mml/csd/organic/vitamindinserum.cfmexternal link disclaimer
    SRMsexternal link disclaimer can be used as "trueness" controls, e.g., SRM 972a, and calibrators, e.g., SRM 2972.
  • Centers for Disease Control and Prevention (CDC) Vitamin D Standardization Certification Program.
    http://www.cdc.gov/labstandards/hs.htmlexternal link disclaimer
    Most clinical and research laboratories measure total 25(OH)D using commercially developed assays. Laboratories using commercial assays must perform them rigorously as recommended by the manufacturer, but otherwise have very little control over how those assays function in comparison to RMPs. As such, commercially developed assays play a central role in the entire standardization effort. Moreover, as certification lasts for only one year, the maintenance of certification requires ongoing participation.
  • Accuracy-Based Quality Assurance Programs.
    The CDC program is not a practical solution for routine clinical and research laboratories. For such laboratories, accuracy-based performance testing or external quality assessment (EQA) schemes are available, i.e., College of American Pathologists Accuracy-Based Vitamin D (ABVD) program and Vitamin D External Quality Assessment Scheme (DEQAS). 
  • Study designs for standardizing completed studies
    Statistical procedures for standardizing 25(OH)D measurements from completed studies have been developed by the VDSP.* The procedures include methods for calculating sample size and for selecting samples to be re-measured. In the near future we will include links to manuals with instructions for using the VDSP statistical procedures.

* Cashman KD, Kiely M, Kinsella M, et al. Am J Clin Nutr 2013;97:1235-42external link disclaimer.