[Osteocalcin and bone histology in osteoporosis].

The decoupling of bone formation and bone resorption causes an insidious bone loss that is responsible for the negative skeletal balance in the frequent form of low turnover osteoporosis. The reduction of bone formation can hardly be verified by clinical methods. Osteocalcin, a non-collagenous bone protein, has proved to be a useful new indicator of bone formation. To establish its predictable value, plasma levels of osteocalcin were compared to conventional serological data of bone turnover and to histomorphometric parameters of iliac crest trabecular bone. In cases of osteoporosis with normal bone turnover activity (as confirmed by histomorphometry) no differences were observed in any of our laboratory data including osteocalcin. However, there was a significant lower mean serum level of osteocalcin in a group of patients with histomorphometrically proven low turnover osteoporosis in comparison to those with normal bone turnover. Serum levels of osteocalcin below 2.0 ng/ml seem to indicate a low turnover in the individual case of osteoporosis while this is unlikely when serum levels above 6.0 ng/ml are measured (according to our RIA).