Radioimmunoassay of Osteocalcin with Polyclonal and Monoclonal Antibodies

We have developed and thoroughly validated radioimmu-noassays (AlAs) for osteocalcin in plasma and serum, dem-onstrating independence of volume and determining the recovery of added standard and within- and between-assay precision. Antibodies were raised in rabbits and mice by immunization with either osteocalcin adsorbed to poly-vinylpyrrolidone or osteocalcin conjugated to bovine serum albumin. In both species, use of the conjugated osteocalcin was more efficacious. Correlation of the results obtained when groups of plasma or serum samples were analyzed by AlAs with different antibodies (two polyclonal and one mono-clonal) indicated that the normal range observed for osteo-calcin concentrations in serum depends on the antibody used. These findings may account for the wide range of “normal ” osteocalcin values reported by different groups