I-Vitamin D iyivithamini futhi iyi-hormone ye-steroid, ikakhulukazi ehlanganisa i-VD2 ne-VD3, imiyalelo yayo efana kakhulu. I-Vitamin D3 kanye ne-D2 iguqulwa ibe yi-25 hydroxyl vitamin D (kuhlanganise ne-25-dihydroxyl vitamin D3 kanye ne-D2). I-25-(OH) VD emzimbeni womuntu, ukufundisa okuzinzile, ukugxila okuphezulu. I-25-(OH) VD ibonisa inani eliphelele likavithamini D , kanye nekhono lokuguqulwa likavithamini D, ngakho-ke i-25-(OH)VD ibhekwa njengenkomba engcono kakhulu yokuhlola izinga likavithamini D. Ikhithi Yokuxilongwa isekelwe i-immunochromatography futhi inganikeza umphumela kungakapheli imizuzu eyi-15.