The National Institute of Standards and Technology (NIST) and the National Institutes of Health (NIH) Office of Dietary Supplements (ODS) established a Vitamin D Metabolites Quality Assurance Program (VitDQAP). Interlaboratory comparison studies were directed toward the measurement of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, and 3-epi-25-hydroxyvitamin D3 in selected serum and plasma matrices as well as method-appropriate control materials. The VitDQAP concluded in 2015, and parts of the VitDQAP community will now be served through the HAMQAP.
NIST Vitamin D Metabolites Quality Assurance Program (VitDQAP) supported the reliability of vitamin D measurements in human serum and plasma. Results from the comparison studies helped participants to make accurate clinical and health-care decisions as well as to maintain and improve their measurement comparability.
The Vitamin D Metabolites Quality Assurance Program (VitDQAP) at NIST administered 12 interlaboratory comparison exercises for the measurement of vitamin D metabolites in human serum and plasma. The comparability of laboratory measurements for target analytes improved substantially over time through the development and promulgation of robust measurement technologies, identification and production of suitable reference materials, isolation and identification of measurement system biases, and support and encouragement of within-laboratory measurement quality control efforts. A final report for the VitDQAP is provided here.
An example figure from the Summer 2011 Report illustrating the 25-hydroxyvitamin D (25(OH)DTotal) levels in two study materials as determined by immunoassay (CLIA, EIA, and RIA) and LC (LC-MSn and LC-UV) methods is shown below.
Reports for the twelve exercises have been published:
Certificates of participation can also be provided upon individual request.
VitDQAP workshops (or webinars) were held for laboratories that measured vitamin D metabolites in human serum and plasma as part of the QA program. These workshops provided an opportunity for participants to discuss analytical methods, results of the interlaboratory comparison exercises, and other related topics.
Standard Reference Material (SRM) 972a and SRM 2972a
We recommend that laboratories use Standard Reference Materials (SRMs) such as SRM 972a Vitamin D Metabolites in Human Serum and SRM 2972a 25-Hydroxyvitamin D Calibration Solutions to validate their methodology and to value assign in-house control materials. SRMs for fat-soluble vitamins in human serum and plasma may be purchased from the Office of Reference Materials at NIST (301-975-2200; fax: 301-948-3730; or e-mail: srminfo [at] nist.gov).
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Frozen or freeze-dried serum or plasma samples together with control materials were sent to laboratories biannually (winter and summer) for analysis. Results were then returned to NIST for data evaluation and tabulation. Value-assignment of the samples was based on the median of all the laboratory results, with confirmation based on measurement at NIST using one or more different methods. Consultation and troubleshooting regarding methods of analysis were also provided. A report of exercise results was sent to participants, and workshops were scheduled periodically to discuss results as well as methodological issues and advancements in clinically-relevant vitamin D metabolite measurements.