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) in 2009. The VitDQAP conducted 12 exercises before concluding in 2015. Parts of the VitDQAP community were served through the HAMQAP from 2017 to 2021, and are now served through the ClinQAP.
Interlaboratory comparison studies of the VitDQAP supported the reliability of vitamin D measurements, including determination of 25-hydroxyvitamin D2, 25-hydroxyvitamin D3, and 3- epi-25-hydroxyvitamin D3 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 VitDQAP 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. The major accomplishments of VitDQAP have been summarized in a final report.
An example figure from the Summer 2011 Report illustrates 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.
Reports for intercomparisons are available as NIST Interagency/Internal Reports (IRs):
Certificates of participation are also available upon individual request
VitDQAP workshops (or webinars) were held periodically, providing an opportunity for participants to discuss analytical methods, results of the interlaboratory comparison exercises, and other related topics.
NIST has developed a number of Standard Reference Materials (SRMs®) that are intended for use in validating methods for determining vitamin D metabolites in human serum and qualifying control materials produced in-house and analyzed using those methods.
These SRMs may be purchased from the Office of Reference Materials at NIST.
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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.