[Osteocalcin or bone GLA-protein].

Osteocalcin or GLA bone protein, the most abundant of non-collagen proteins in bone, is produced only by osteoblasts. Synthesis is enhanced by the active form of vitamin D. Most of the osteocalcin produced combines with hydroxyapatite crystals, but a small proportion is circulated in the bloodstream and eliminated by the kidneys. Because bone resorption and bone formation are closely linked, serum osteocalcin is a specific and reliable marker of bone tissue activity.