[Radiocompetitive estimation of 25-hydroxyvitamin D in human serum (author's transl)].

A radiocompetitive estimation of 25-hydroxyvitamin D in human serum is described. After extraction, a stage of purification by chromatography on a Sephadex LH 20 column permits separation of 25-hydroxyvitamin D from Vitamin D and other metabolites. The reaction of radiocompetition uses as tracer tritiated 25-hydroxycholecalciferol and as source of binding protein, rat renal cytosol. The characteristics of the binding protein and the presence in human plasma of significant quantities of 24,25-dihydroxyvitamin D render necessary the chromatographic stage. This technic permits one to measure simply and specifically 25-hydroxyvitamin D in the human serum, of which normal levels (average +/- standard deviation) are 12.88 +/- 5.42 microgram/l 3.2.10(-8) + 1.35.10(-8) mol/l).