Determination of bone Gla protein (osteocalcin) by enzyme-linked immunosorbent assay

Bone Gla protein (BGP, osteocalcin) is a marker of bone formation. We present a novel enzyme-linked immunosorbent assay for measuring BGP in plasma and serum. The antibody used was raised in rabbits following immunisation with highly purified bovine BGP conjugated with keyhole limpet hemocyanin. The binding of the antibody to BGP was calcium-dependent. The sensitivity, inaccuracy, and imprecision of the assay equal or exceed existing radioimmunoassays, and the present assay is less tedious. Plasma BGP in 249 healthy adults, aged from 20 to 93 yr, was 8.3 +/- 6.6 micrograms/l (mean +/- 2 SD). A significant decrease was seen in both sexes from the third to the forth decade of life. A subsequent significant increase was seen with age in women. but not in men. Plasma BGP was significantly higher in young men than in young women, and significantly higher in elderly women than in elderly men. Values were in the same range as those found with existing radioimmunoassays.