Serum osteocalcin radioimmunoassay in bone diseases.

Osteocalcin (or bone Gla protein, BGP) is a non-collagenous vitamin K-dependent protein accounting for 1-2% of the total bone proteins. It represents a specific index of osteoblastic activity and directly reflects the bone turnover. Serum levels of osteocalcin were measured by a radioimmunoassay method. In 40 postmenopausal women with osteoporosis, mean serum BGP levels were lower than the normal range (3.69 +/- 1.35 ng/ml), whereas they significantly increased in 7 patients with osteomalacia (10.48 +/- 3.05 ng/ml), in 12 patients with secondary hyperparathyroidism (11.1 +/- 4.9 ng/ml) and in 41 patients with Paget's disease (12.09 +/- 6.5 ng/ml). Four patients with primary hyperparathyroidism showed very high BGP levels (64.0 +/- 32.3 ng/ml), which strikingly fell after the surgical removal of a parathyroid adenoma. These results confirm that the quantitation of serum osteocalcin is a specific and sensitive method in the diagnosis of bone disease, represents a useful index of bone turnover and is particularly helpful in the follow-up of patients with treated bone disease.