Commercial Assays for Serum Osteocalcin Give Clinically Discordant Results

Serum samples from 9 healthy controls and from subjects with primary hyperparathyroidism (n = 5), Paget disease (n = 3), pregnancy (n = 5), glucocorticoid therapy (n = 5), postmenopausal osteoporosis (n = 10), and renal failure (n = 10) were used to assess the clinical agreement among eight commercially available assay kits for osteo-calcin (OC). These kits differ in their assay configurations (six radioimmunoassays, two immunoradiometric as-says), standards (five bovine, three human), and antibod-ies (six polyclonal, two monoclonal). Individual results were divided by the mean OC of the control subjects for each assay and expressed as percentage deviations. The expected wide variation in absolute OC concentrations between kits was only partially reduced by this transfor-mation. Agreement was equally poor when absolute O