Calcitriol D2 Unit Converter

1,25-Dihydroxyvitamin D2 is the fully activated hormonal form of vitamin D2 (ergocalciferol). It is the D2 counterpart of calcitriol (1,25-dihydroxyvitamin D3), which is the active form of vitamin D3.

Total circulating 1,25-dihydroxyvitamin D is the sum of the D2 and D3 fractions. Standard lab tests measure the combined total, while specialized LC-MS/MS testing can separate and quantify each fraction individually.

Because vitamin D3 is the form produced by human skin and found in most animal-derived foods, 1,25-dihydroxyvitamin D2 is typically undetectable in people who are not taking vitamin D2 supplements or consuming significant amounts of UV-irradiated mushrooms. Established clinical reference ranges apply only to total 1,25-dihydroxyvitamin D (D2 + D3 combined), not to the D2 fraction alone.

Vitamin D2 (ergocalciferol) is obtained from dietary or supplemental sources such as UV-irradiated mushrooms, fortified foods, and prescription ergocalciferol capsules. It is converted to 25-hydroxyvitamin D2 in the liver, then activated to 1,25-dihydroxyvitamin D2 by the enzyme CYP27B1 primarily in the kidneys.