The value of biochemical markers of bone turnover in osteoporosis.

A number of biochemical markers of bone turnover have been described and these reflect the activity of osteoblasts (bone formation) or osteoclasts (bone resorption). These markers have the following advantages for the measurement of bone turnover: (1) they are noninvasive; (2) inexpensive; (3) can be repeated on many occasions; (4) and reflect bone cell activity in the entire skeleton. They have disadvantages: (1) they do not provide information about the work of individual cells; (2) they do not reflect the process of mineralization; and (3) their levels may be affected by the rate of clearance. The markers have been used to study the pathogenesis of osteoporosis, identify postmenopausal women with accelerated bone loss, predict fracture independently of bone loss, predict response to therapy, and monitor response to therapy. They may also be useful in the setting of clinical trials for choosing minimal and maximal effective doses, understanding the mechanism of the changes in bone mineral density (BMD) and studying the effect and time course of changes in bone after cessation of therapy. Markers do not provide a surrogate for fracture risk or BMD. However, they do have uses in osteoporosis and can provide preliminary data in the short term that can be used in the design of longterm studies of BMD and fracture.