What does alkaline phosphatase indicate in bone turnover assessment?

• A. Marker of bone resorption.
• B. Marker of bone formation.
• C. Marker of calcium absorption in the gut.
• D. Direct measure of bone mineral density.

Answer: (B)

Alkaline phosphatase signals bone formation because it is produced by osteoblasts during new bone synthesis. It plays a role in mineralization by helping provide phosphate for the mineral crystals that harden bone, so higher activity reflects more osteoblastic formation.

In bone turnover assessment, a rise in alkaline phosphatase indicates increased bone formation activity, seen in growing children, during fracture healing, or in high-turnover bone disorders. It isn’t a measure of bone resorption—that’s tracked by other markers like CTX or NTX—and it isn’t a direct measure of bone mineral density. Also, since total alkaline phosphatase can come from liver, using the bone-specific isoform helps avoid misinterpretation.