Vitamin D

Vitamin D

Vitamin D Background (Why we are interested in Vitamin D standardization)

The Institute of Medicine and other expert groups concluded that a single individual might be deemed deficient or sufficient, depending on the laboratory where the blood is tested. This problem is caused mainly by inaccurate and unreliable vitamin D tests used in these laboratories. Over 1,000 clinical laboratories perform vitamin D testing in the U.S. Some of these laboratories perform over 61,000 vitamin D tests per month. Testing for Vitamin D deficiency and supplementation has been increasingly advocated in the past decade. As a result, the volume of vitamin D tests given to Medicare patients alone increased dramatically by a factor of 83 between 2000 and 2010. Thus, inaccurate vitamin D testing can lead to large numbers of people being misdiagnosed.

Standardization Activities for Vitamin D (What is currently being done to standardize Vitamin D)

Several coordinated efforts to improve and assure the accuracy of vitamin D testing in patient care and research are under way by the National Institute of Health (NIH), the Centers for Disease Control and Prevention (CDC), the National Institute for Standards and Technology (NIST), the University of Ghent, the College of American Pathologists (CAP), and the Vitamin D External Quality Assessment Scheme (DEQAS) in the United Kingdom.

As part of its Vitamin D Initiative, the NIH Office of Dietary Supplements (NIH/ODS) established the Vitamin D Standardization Program (VDSP). One of the objectives of VDSP is to standardize the measurement of serum total 25(OH)D in national health surveys by linking it to the NIST reference measurement procedure;  VDSP will then study similarities and differences in total 25(OH)D among national health surveys. To meet these objectives, the NIH/ODS is collaborating with several research centers around the world that are conducting national health surveys, and it is supporting the NIST to develop and maintain reference methods and materials for vitamin D and its metabolites. Furthermore, it is supporting DEQAS to promote accuracy-based proficiency testing.

The CDC is supporting the VDSP by standardizing assay manufacturers and clinical and research laboratories through its Vitamin D Standardization Certification Program (VDSCP). This program provides reference measurement services to laboratories and assay manufactures, and it evaluates and certifies measurement performance of its participants. The CDC is collaborating with the College of American Pathologists (CAP) on its accuracy-based vitamin D survey. In addition, it is collaborating to standardize measurements performed in the National Health and Nutrition Examination Survey (NHANES).

Because of the high demand for reference measurements, reference laboratories are established at NIST, CDC, and the University of Ghent. The reference laboratory at the University of Ghent, operated by Prof. Dr. Linda Thienpont, provides reference measurement services for the clinical laboratory community. All three laboratories provide comparable results and help to assure that the vitamin D measurements performed in research, patient care, and public health are accurate and comparable across methods and laboratories, and over time.