MEASUREMENT OF 1,25‐DIHYDROXYCHOLECALCIFEROL IN MAN BY RADIOIMMUNOASSAY

Abstract

1α,25-dihydroxycholecalciferol (1,25-(OH)₂D₃) has been measured in human serum by radioimmunoassay. The assay uses a high titre antiserum raised in sheep against 1,25-(OH)₂D₃-25-hemisuccinate, conjugated to bovine serum albumin. The sensitivity of the assay is 10 pg/tube. Other hydroxylated forms of vitamin D₃ cross react with the antiserum and are therefore removed from serum extracts by chromatography on Sephadex LH 20 followed by high pressure liquid chromatography. The mean (± SEM) serum 1,25-(OH)₂D₃ concentration for a group of healthy adult subjects was 41 ± 2.5 pg/ml. None was detected in anephric patients and the concentration was low or undetectable in patients with chronic renal failure.