Circulating vitamin D is most commonly reported as a total of 25(OH)D2 and 25(OH)D3, reported as 25(OH)D.
The most common biomarker used to assess vitamin D status is 25-hydroxy vitamin D 25(OH)D, reported as a total of 25(OH)D2 and 25(OH)D3. Circulating 25(OH)D is considered the general reservoir or inactive “storage” form of vitamin D. The ODX software ranges reflect total 25(OH)D.
It should be noted that the LC/MS/MS method reports D2 and D3 metabolites of 25(OH)D separately as well as reporting the total 25(OH)D, whereas the immunoassay reports the total 25(OH) D2 and D3 together without differentiation (Quest Diagnostics).
Please refer to past ODX publications for more information:
Method of measuring vitamin D
Vitamin Biomarkers: Vitamin D
https://www.optimaldx.com/research-blog/vitamin-biomarkers-vitamin-d
Vitamin D: Optimal Levels and How to Get There
https://www.optimaldx.com/blog/vitamin-d-optimal-levels-and-how-to-get-there
Quest AssureD LC/MS/MS Test Details
- Vitamin D, 25-OH, Total
- Vitamin D, 25-OH, D3
- Vitamin D, 25-OH, D2
Quest Diagnostics total vitamin D via Immunoassay: