Bone biomarkers as tools in osteoporosis management.

Biochemical tests that can index bone turnover rate in the patient are increasingly being used in the study and management of osteoporosis. Markers of bone formation and resorption are reviewed here, including their molecular basis, relative strengths and weaknesses in clinical performance, and future potential. A bone mass measurement (e.g., by dual-energy x-ray absorptiometry) and a biochemical index of bone turnover provide different but complementary information that can aid in predicting risk of future bone loss and osteoporotic fracture. A specific and responsive bone resorption marker can also be used to monitor and establish the short-term effectiveness of an antiresorptive therapy in the patient. Bone-specific alkaline phosphatase (an osteoblast enzyme) and osteocalcin (a bone matrix protein) levels in serum are the best markers of bone formation. Collagen degradation products in urine, particularly cross-linked telopeptides and pyridinolines, have the highest specificity to bone resorption activity. The telopeptide markers (NTx and CTx) appear to be the most specific and responsive markers of systemic osteoclast activity.