New markers of bone metabolism: clinical use in metabolic bone disease

Bone remodeling constitutes the life-long renewal process of bone whereby the mechanical integrity of the skeleton is preserved. It implies the continuous removal of bone (bone resorption) followed by synthesis of new bone matrix and subsequent mineralization (bone formation). Moreover, bone remodeling is an integral part of the calcium homeostatic system together with the kidneys and the gut. The ever ongoing removal of old bone by osteoclastic resorption and subsequent coupled osteoblastic formation of new bone leads to liberation of calcium and matrix constituents into the serum. The matrix constituents liberated into the blood during bone resorption can be used as markers of bone resorption in serum or urine and components liberated during osteoblastic matrix synthesis are putative markers of bone formation.Extensive research over the last 10 years has characterized a wide variety of new markers of cellular activity in bone (Table 1). Serum and urine levels of these