 At a typical daily intake of vitamin D3, its full conversion to calcifediol takes approximately 7 days.Calcifediol is then converted in the kidneys (by the enzyme 25(OH)D-1α-hydroxylase) into calcitriol (1,25-(OH)2D3), a secosteroid hormone that is the active form of vitamin D. It can also be converted into 24-hydroxycalcidiol in the kidneys via 24-hydroxylation.In medicine, a 25-hydroxy vitamin D (calcifediol) blood test is used to determine how much vitamin D is in the body.