Vitamin D Standardization-Certification Program

At a glance

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.

Healthy children

Standardization of Vitamin D

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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 ages 50 years and older will have an osteoporosis-related fracture in their lifetime.1

Vitamin D tests are used to determine a person’s vitamin D status and to aid in the diagnosis of diseases associated with bone metabolism and diseases such as cystic fibrosis and Crohn disease. Vitamin D is among the most commonly requested laboratory tests. These tests must be accurate to ensure correct diagnoses and treatment of patients with vitamin D deficiency.

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 work to:

  • Provide reference measurements for total 25-hydroxyvitamin D. [Vitamin D Reference Laboratory]
  • Assess and certify the analytical performance (accuracy and precision) of vitamin D tests used in patient care, research and public health. [Improving Performance - VDSCP]
  • Monitor the accuracy of measurements performed in routine laboratories over time. [Monitoring Accuracy - AMP Vitamin D]
  • Provide technical support to external quality assurance programs, proficiency testing programs, and research studies that ensure vitamin D tests are accurate and reliable.
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Graph shows the difference between the mean bias among VDSCP participants.
Improvement in *Mean Bias Among VDSCP Participants

More on Vitamin D and the CDC VDSCP

What is Vitamin D?

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.

How is vitamin D status assessed?

Blood tests for assessing a person's vitamin D status measure two forms: 25-hydroxyergocalciferol (25-hydroxyvitamin D2) and calcifediol (25-hydroxyvitamin D3). These reflect the cumulative effects of exposure to sunlight and dietary intake of vitamin D--the two ways people get vitamin D. Clinicians use the tests to determine one's vitamin D status.

What Does the Vitamin D Reference Method Laboratory Do?

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.

What is the Vitamin D Standardization-Certification Program?

CDC's Vitamin D Standardization-Certification Program evaluates the accuracy and reliability of vitamin D tests using well-established procedures. We certify those that have a certain level of accuracy and precision.

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Content Source:
National Center for Environmental Health; Division of Laboratory Sciences