A SIMPLIFIED ASSAY FOR DIHYDROXYLATED VITAMIN-D METABOLITES IN HUMAN-SERUM - APPLICATION TO HYPERVITAMINOSIS-D AND HYPOVITAMINOSIS-D

Abstract

A simplified assay is described for 24,25- and 1,25-dihydroxyvitamin D in human serum. It involves 2 preparative steps, and normal chick intestine is used in preparing cytosol-binding protein. Results for 24,25-dihdryoxyvitamin D include a reference interval of 2.9-16 nmol/l (1.2-6.7 .mu.g/l), a mean of 6.7 nmol/l (2.8 .mu.g/l), an intra-assay CV [coefficient of variability] of 11% and an interassay CV of 22%. For 1,25-dihydroxyvitamin D, these data were 29-168 pmol/l (12-70 ng/l), 86 pmol/l (36 ng/l), 12% and 22%, respectively. In hypoparathyroid patients with vitamin D intoxication, mean concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D in serum were significantly above normal; the 1,25-dihydroxyvitamin D concentrations were significantly below normal. Patients with malabsorption and/or post-gastrectomy states had significantly subnormal values for 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D in serum; there was a significantly negative correlation between each biochemical value and the severity of osteomalacia. Cost effectiveness of assaying vitamin D metabolites in human serum is discussed.