Can serum osteocalcin levels predict bone turnover in patients with osteoporosis?

The assessment of bone metabolism by biochemical markers remains difficult problem. Serum osteocalcin, synthesized in bone cells, is now becoming a sensitive indicator of bone turnover in patients with metabolic bone diseases. We measured serum osteocalcin levels by radioimmunoassay in 18 patients with osteoporosis and examined whether they reflect bone formation, resorption or both. We found that serum osteocalcin levels in biopsy-identified osteoporotics were widely ranged (1.8 – 18.8 ng/ml). Tetracycline double labeling method exibited two types of labeling pattern in the iliac bone, that is double labeled or no double labeled (impaired labeled) pattern. Serum concentrations of osteocalcin in patients with double labeling were significantly higher than those with impaired labeling (11.2±4.0 vs 4.1 ±2.1 ng/ml, P<0.01). Furthermore, serum osteocalcin levels showed a significantly positive linear correlation with the parameters reflecting bone formation, but not with bone resorption. These data indicate that serum osteocalcin levels reflect bone formation in osteoporotics and thereby could be a useful indicator of osteoblastic function in osteoporosis.