Evaluation of a bead-based enzyme immunoassay for the rapid detection of osteocalcin in human serum

Background: Circulating osteocalcin is a well-known marker for bone formati on, but none of the commercial kits currently available can be used in auto mated systems. Here we present the first semiautomated assay for human seru m osteocalcin. Methods: Polystyrene beads were coated with antibodies against the COOH ter minus of osteocalcin and used in the COBAS(R) EIA System. Osteocalcin was d etected with peroxidase-conjugated antibodies against the osteocalcin NH2 t erminus. Results: The time required to analyze an unknown sample was 60 min, with a lower detection limit of 4.5 mu g/L and a linear dose-response curve betwee n 4.5 and 100 mu g/L. The intraassay imprecision (CV) was 5-8% (n = 21); th e interassay variation was 6-9% (n = 14). In samples from human volunteers and patients, data generated with the newly developed assay were comparable to those obtained with standard microtiter plate-based assays. Conclusions: The coated beads assay may be implemented on fully automated a nalyzers, which not only may further reduce imprecision but may also substa ntially increase the applicability of osteocalcin as a marker for bone meta bolism in the routine clinical setting. (C) 2000 American Association for C linical Chemistry.