Plasma levels of bone Gla-protein reflect bone formation in patients on chronic maintenance dialysis

Predictive value of plasma levels of bone Gla-protein (BGP) for bone histology was evaluated in 30 chronically dialyzed patients. All patients underwent bone biopsies and serum biochemical parameters, including BGP, parathyroid hormone, and alkaline phosphatase; calcium and phosphate were measured at the time of biopsy. Bone histology showed renal osteodystrophy with low bone turnover and osteomalacia (LT-ROD) in 13 patients, and renal osteodystrophy with high bone turnover and prevailing hyperparathyroid bone disease (HT-ROD) in 17 patients. Values for BGP were above normal in LT-ROD (47.3 +/- 7.9 vs. 6.8 +/- 0.2 ng/ml) and extremely elevated in HT-ROD (831 +/- 170 ng/ml). Similar differences were not found with the other serum biochemical parameters, even though BGP correlated with parathyroid hormone (r = 0.64) and alkaline phosphatase (r = 0.85). There were significant correlations between BGP and cellular and non-cellular parameters of bone formation (r = 0.73 to 0.91). Weaker or no correlations were found between BGP and histologic parameters of bone, reflecting mainly mineralization or resorption. These correlations and the finding of significant differences in plasma BGP between LT-ROD and HT-ROD indicate that plasma levels of BGP reflect bone formation in uremia and predict underlying bone histology.