VDSCP: Vitamin D Standardization-Certification Program
Osteoporosis and other bone diseases affect millions of U.S. residents and are a major cause of disability. Half of all women and as many as a quarter of men age 50 years and older will have an osteoporosis-related fracture in their lifetime.1
Vitamin D is an essential nutrient long-known for its role in maintaining bone health. People who are deficient in vitamin D are at higher risk for osteoporosis. Laboratory tests for vitamin D are used to determine a person’s vitamin D status, and to identify persons with vitamin D deficiency. These tests must be accurate to ensure correct diagnoses and treatment of patients with vitamin D deficiency.
The Centers for Disease Control and Prevention (CDC) improves the detection and diagnosis of bone diseases by ensuring that laboratory tests for vitamin D are accurate and reliable. CDC’s Vitamin D Reference Method Laboratory and the Vitamin D Standardization–Certification Program (VDSCP) work to
- provide reference measurements for total 25-hydroxyvitamin D (sum of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3),
- assess the accuracy and precision of vitamin D tests, and monitor their performance over time, and
- provide technical support to external quality assurance programs, proficiency testing programs, and research studies that ensure vitamin D tests are accurate and reliable.
The biologically active form of vitamin D (1,25-dihydroxyvitamin D) is a hormone whose main function is to keep serum calcium and phosphorus concentrations in blood within normal ranges.
In patient care and public health assessments, vitamin D is defined as the sum of 25-hydroxyergocalciferol (25-hydroxyvitamin D2) and calcifediol (25-hydroxyvitamin D3). Our bodies convert both compounds to 1,25-dihydroxyvitamin D. Levels of 25-hydroxyergocalciferol and calcifediol in blood describe a person’s vitamin D status.
Blood tests for assessing a person’s vitamin D status measure two forms: 25-hydroxyergocalciferol (25-hydroxyvitamin D2) and calcifediol (25-hydroxyvitamin D3). These major circulating forms reflect the cumulative effects of exposure to sunlight and dietary intake of vitamin D (the two ways people get vitamin D), and therefore, clinicians use them to determine vitamin D status.
CDC’s Vitamin D Reference Laboratory uses a highly accurate and precise reference method for measuring 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 (total 25-hydroxyvitamin D). It uses this reference method to assign reference values to serum samples.
CDC’s Vitamin D Standardization-Certification Program (VDSCP) evaluates the accuracy and reliability of vitamin D tests using well-established procedures, and certifies those that have a certain accuracy and precision.
Standardization is an activity in which the accuracy, precision, and other analytical performance parameters of a laboratory test are assessed against analytical performance goals by an independent, impartial, qualified organization. Thus, a standardized laboratory test is a test that demonstrated, through an independent and impartial assessment, an analytical performance, such as accuracy and precision, which meets specific analytical performance goals.