A binding assay for 25-hydroxycalciferols and 24R,25-dihydroxycalciferols using bovine plasma globulin.

The concentrations of the 25-hydroxy and 24R, 25-dihydroxy derivatives of vitamin D were determined in 100 microliter l plasma samples using calciferol binding globulin from bovine plasma. Sufficient quantities of 24R, 25-dihydroxy vitamin D were found in bovine, porcine, chicken and human plasma to interfere in the assay of 25-hydroxy vitamin D in unfractionated extracts. No metabolites of vitamin D could be found in rainbow trout plasma.