Description General description 25-hydroxyvitamin D3 (calcifediol) is a prohormone produced via hydroxylation of vitamin D3 (cholecalciferol) in the liver. It is a precursor for the synthesis of calcitriol or 1,25-dihydroxyvitamin D3 or [1,25(OH)2D3]. It is used as a biomarker to determine the status of vitamin D in the body. 25-Hydroxyvitamin D3 (6,19,19-d3) is a deuterated 25-hydroxyvitamin D3 wherein C-6 and C-19 protons are replaced by deuterium. Application 25-Hydroxyvitamin D3 (6,19,19-d3) can be used as an analytical standard for the quantitative analysis of hydroxyvitamin D3 concentration in human serum via LC-MS. Packaging 1 mL in ampule