Which biomarker is used to monitor bone resorption and is measured in osteoporosis assessments?

• A. Osteocalcin
• B. Tartrate-resistant acid phosphatase
• C. Cross-linked C-telopeptides
• D. Alkaline phosphatase

Answer: (C)

Bone turnover markers include substances released during bone formation and bone resorption. In osteoporosis management, tracking resorption helps gauge how quickly bone is being lost and how well a treatment slows it. Cross-linked C-telopeptides of type I collagen are fragments released when bone collagen is broken down, so measuring them in blood or urine provides a direct readout of resorption activity. Because CTX levels respond quickly to changes in resorption, they’re widely used to monitor how well antiresorptive therapies are working. Osteocalcin, in contrast, reflects bone formation, not resorption. Alkaline phosphatase mainly indicates bone formation (bone-specific ALP is more specific but still a formation marker), and tartrate-resistant acid phosphatase is another osteoclast-related marker but CTX is the standard in osteoporosis assessments.