A one step sandwich enzyme immunoassay for γ-carboxylated osteocalcin using monoclonal antibodies

A highly sensitive, simple and reliable one-step sandwich enzyme immunoassay (EIA) for the γ-carboxylated form of osteocalcin (Gla-OC) has been developed using a monoclonal antibody. The minimum amount of Gla-OC detected by this EIA was approximately 0.2 ng/ml when a 10 μl aliquot of the sample was used. The serum Gla-OC level in 30 healthy subjects was 3.6 ± 2.19 ng/ml (mean) ± SD. A significant increase was seen in patients with chronic renal failure (20.3 ± 4.60 ng/ml), atherosclerosis (8.3 ± 4.94 ng/ml) and osteoporosis (10.1 ± 4.60 ng/ml). The correlation between the values obtained by the sandwich EIA and competitive RIA methods was given by the linear regression equation, y = 2.896 + 0.759 x, for which the correlation coefficient ( r) was 0.815 ( n = 58). This newly developed Gla-OC specific EIA may be useful for the diagnosis of metabolic bone disease and ectopic calcification.