Vitamin D is measured with 25OHD


Among the various forms of vitamin D described above, the level of 25(OH)D is the best indicator of vitamin D status and stores.

25(OH)D is the main circulating form of vitamin D, and has a half life of two to three weeks. In contrast, 1,25(OH)2D has a much shorter half life of about four hours, circulates in much lower concentrations than 25(OH)D, and is susceptible to fluctuations induced by PTH in response to subtle changes in calcium levels.