[Simultaneous radiocompetitive assay for 25 hydroxyvitamin D and 24, 25 dihydroxyvitamin D in human serum (author's...

A specific competitive protein binding assay for 25 hydroxy-vitamin D and 24, 25 dihydroxyvitamin D in human serum has been developed. It includes a chromatographic step on a Sephadex LH 20 column to specifically separate the metabolites. The average value was for 25 hydroxyvitamin D 11.9 +/- 6.6 Ng/ml (mean +/- SD) and for 24, 25 dihydroxyvitamin D 6.85 +/- 3.29 ng/ml in ten normal subjects sampled in autumn. In hepatic insufficiencies the mean level of 25 hydroxyvitamin D was lower and the mean level of 24, 25 dihydroxyvitamin D was higher than in normal subjects. In patients with renal insufficiency the 25 hydroxyvitamin D levels were normal and the 24, 25 dihydroxyvitamin D levels were low but not suppressed. The two sterols were also determined in some patients with idiopathic hypercalciuria.