[Assay of fat-soluble vitamins--vitamin D]

Methods for determination of vitamin D, 25-OH-D, 24,25(OH)2D and 1,25(OH)2D in plasma are reviewed. A method for simultaneous determination of the D2 and D3 compounds of vitamin D and the metabolites in plasma is established. The method includes extraction of lipid, followed by three steps of HPLC for clean-up and separation. Vitamin D and 25-OH-D are quantified by HPLC with a UV detector, while 24,25(OH)2D and 1,25(OH)2D are assayed by CPBA and RRA methods, respectively. The assayed values for concentrations of the compounds in plasma of normal subjects and various kinds of patients are shown. A simplified method for assaying 1,25(OH)2D in plasma using calf thymus receptor is also introduced.