Radioimmunoassay for 1,25-dihydroxycholecalciferol

Abstract

This radioimmunoassay has several unique features: a stable binding protein (the antiserum), short assay incubation, and an efficient procedure for the isolation of 1,25(OH)2D3 from serum. Analysis of the raw data by a computer program can further reduce the time and effort expended. The limited specificity of the antiserum for 1,25(OH)2D3 relative to the other metabolites of vitamin D3 is a drawback. However, the generation of antibodies with immunoreactivity against the 1α-hydroxyl function of the A ring will remove this limitation. Our preliminary experience with 1α-hydroxycholecalcioic acid as hapten has produced antisera with greater specificity for the 1α-hydroxyl position on the A ring. When such highly specific antisera are widely available, the radioiummunoassay of 1,25(OH)2D3 will be the analytical method of choice.