From the Guidelines
To monitor vitamin D deficiency, you should order the 25-hydroxyvitamin D (25(OH)D) blood test, which measures both 25(OH)D2 and 25(OH)D3 levels. This is the standard and most accurate test for assessing vitamin D status in the body, as recommended by a panel of experts in a study published in Autoimmunity Reviews 1. When ordering this test, specify "25-hydroxyvitamin D" rather than "vitamin D" to ensure you get the correct measurement.
Key Considerations
- Normal levels typically range from 30-100 ng/mL (75-250 nmol/L), with levels below 20 ng/mL indicating deficiency, although a target range of at least 30 to 40 ng/mL was recommended by the study 1.
- For patients with confirmed deficiency, follow-up testing is typically recommended after at least 3 months of supplementation therapy, as response to treatment varies by environmental factors and starting levels of 25(OH)D 1.
- Certain groups, such as dark-skinned or veiled individuals not exposed much to the sun, elderly and institutionalized individuals, may be supplemented (800 IU/day) without baseline testing, but this should be done with caution and consideration of individual patient needs.
Test Characteristics
- The 25(OH)D test is preferred because it has a longer half-life in the bloodstream and better reflects overall vitamin D stores in the body.
- The test measures both 25(OH)D2 and 25(OH)D3 levels, providing a comprehensive assessment of vitamin D status.
From the Research
Monitoring Vitamin D Deficiency
To monitor vitamin D deficiency, the following test is recommended:
- 25-hydroxyvitamin D (25(OH)D) measurement, as it is the accepted measure of vitamin D status 2 This test is used to assess the levels of vitamin D in the body and to determine the effectiveness of vitamin D supplementation.
Factors to Consider
When interpreting the results of the 25(OH)D test, the following factors should be considered:
- The presence of two forms of vitamin D: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3) 2
- The hydrophobic nature of vitamin D, which can affect the accuracy of the test results 2
- The lack of standard calibrators, which can contribute to between-laboratory differences in 25(OH)D measurement 2
Supplementation and Testing
The following studies provide evidence for the use of 25(OH)D testing in monitoring vitamin D deficiency:
- A study published in 2009 found that cholecalciferol supplementation was more effective in increasing serum 25OHD levels than ergocalciferol supplementation in vitamin D-insufficient hip fracture patients 3
- A study published in 2015 found that high-dose ergocalciferol was safe and effective in increasing 25-OH-D levels and suppressing parathyroid hormone levels in stage III-IV CKD patients with vitamin D deficiency/insufficiency 4
- A study published in 2020 found that cholecalciferol has more scientific evidence with positive results than calcifediol in musculoskeletal diseases and is the form of vitamin D of choice in the most accepted and internationally recognized clinical guidelines on the management of osteoporosis 5