Which biomolecule is a marker of bone resorption?

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

Answer: (B)

Bone resorption involves osteoclasts breaking down the bone matrix, mainly type I collagen, and releasing degradation fragments into the blood or urine. Cross-linked C-telopeptides are specific fragments created when collagen is degraded, so their presence and levels directly reflect bone resorption activity. This makes them a reliable marker of resorption. In contrast, osteocalcin and alkaline phosphatase come from osteoblasts and indicate bone formation rather than breakdown, so they don’t measure resorption. Tartrate-resistant acid phosphatase is also linked to osteoclasts, but it’s less commonly used as a standard clinical marker for resorption. Thus, cross-linked C-telopeptides best identify bone resorption.