Bone markers: overuse and much abuse.

Biochemical markers of bone metabolism Historical and current position The cellular activities of the two main bonespecific cell types, osteoblasts and osteoclasts, are tightly coupled and balanced. This balance maintains an adequate amount of bone matrix, which facilitates both the metabolic and physical requirements of bone. While osteoblasts synthesize the organic type 1 collagenous matrix, they also facilitate the inorganically based mineralization of this matrix with calcium phosphate. However, osteoblasts also synthesize marly other non-collagenous proteins which are important in the control and regulation of both themselves and other bone cells. Osteoclasts, the second bone-specific cell type, degrade old bone matrix and release the resulting constituents into the circulation for catabolism and excretion by the kidneys. It is essential, at all times, that both o f these cellular activities are maintained in balance. Bone biochemical markers (Table 1 ) are currently used to monitor these cellular activi-