Which serum marker specifically reflects osteoblastic activity and bone formation rate rather than bone resorption?
- A Tartrate-resistant acid phosphatase isoform 5b
- B Serum C-terminal telopeptide of type I collagen
- C Osteocalcin (bone gla protein) ✓
- D Urinary N-terminal telopeptide of type I collagen
Correct answer: C. Osteocalcin (bone gla protein)
Explanation
Osteocalcin is synthesized exclusively by mature osteoblasts and osteocytes during matrix formation, so serum osteocalcin tracks bone formation. Tartrate-resistant acid phosphatase 5b is released by active osteoclasts, and both C-terminal and N-terminal telopeptides of type I collagen are degradation products liberated when osteoclasts break down bone, making them resorption markers. Total alkaline phosphatase is formation-related but less bone-specific than osteocalcin.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.