Bone density and markers of bone turnover in predicting fracture risk and how changes in these measures predict fracture risk reduction.

Surrogate markers in clinical medicine provide a useful means to assess therapeutic response to pharmacologic therapy in a wide range of chronic disease states. In the area of osteoporosis, the surrogate markers of change in bone mineral density (BMD) and bone turnover markers (BTM) provide the clinician with a means of assessing the biologic response to osteoporosis-specific pharmacologic agents. Increases in BMD and/or reductions in BTM can independently be correlated to reductions in vertebral and nonvertebral fracture risk. In managing osteoporosis patients, the BTM change at an earlier point of time after initiation of therapy and a change in BTM can provide earlier feed-back to the patient and clinician regarding issues such as compliance and a bone biologic response. An increase in BMD at 12 or 24 months after initiation of therapy is also evidence of an improvement in bone strength though with antiresorptive agents no change in BMD may also be associated with risk reduction within clinical trial sets. In this regard, changes in BMD and BTM are complimentary in their application to patient management.