Reference Methods and Materials for Vitamin D Metabolites: Importance for International Data Comparability

Vitamin D has been the subject of intense interest in recent years, not only because of its role in bone health, but also because of the potential link between vitamin D status and the risk of cancer, diabetes, and other diseases. Considerable effort has been devoted to examining the vitamin D exposure of various populations and determining the levels of circulating vitamin D metabolites that are associated with optimal health. Accurate assessment of vitamin D status is also important for identifying individuals with vitamin D deficiencies and for effective treatment. However, the value of vitamin D testing in these applications has been limited by poor comparability between different methods for 25-hydroxyvitamin D [25(OH)D], the major circulating metabolite of vitamin D. In addition, until recently, there was no mechanism to assess the accuracy of any of the methods being used. The Analytical Chemistry Division at the National Institute of Standards and Technology (NIST) is helping to ensure the accuracy and comparability of 25(OH)D measurements through the development of reference methods and Standard Reference Materials (SRMs) for vitamin D metabolites. SRM 972 Vitamin D in Human Serum, and the subsequent SRM 972a Vitamin D Metabolites in Human Serum, represent the first steps toward establishing an accuracy base for measurement of 25(OH)D in individuals and across populations. Value assignment of these reference materials has been performed using multiple higher-order methods. NIST has also initiated a measurement quality assurance program for vitamin D metabolites to assist laboratories in improving accuracy and comparability. Acknowledgements: Partial funding for this work was provided by the National Institutes of Health (NIH), Office of Dietary Supplements (ODS) through an interagency agreement