Metabolic bone disease: bone turnover markers: practice question

A Orthopaedics question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Orthopaedics · Metabolic bone disease: bone turnover markers

Sample item

In monitoring a patient on an antiresorptive drug, which pair correctly identifies a marker of bone resorption and a marker of bone formation?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Serum CTX for resorption and serum P1NP for formation

C-telopeptide of type I collagen (CTX) is released when osteoclasts degrade collagen, so it reflects resorption. Procollagen type I N-terminal propeptide (P1NP) and bone-specific alkaline phosphatase and osteocalcin come from osteoblasts and reflect formation. Antiresorptive drugs such as bisphosphonates lower CTX quickly.

Option by option

  • A. Serum calcium for resorption and serum phosphate for formation

    Serum calcium and phosphate are tightly regulated and are not sensitive markers of turnover.

  • B. Serum P1NP for resorption and serum CTX for formation

    This reverses the markers: P1NP is a formation marker and CTX is a resorption marker.

  • C. Serum CTX for resorption and serum P1NP for formation (correct)

    Correct. CTX is a collagen breakdown product and P1NP is an osteoblast product.

  • D. Bone-specific alkaline phosphatase for resorption and urinary NTX for formation

    Bone-specific alkaline phosphatase is an osteoblast marker, and urinary NTX is a resorption marker, so both roles are reversed.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is C, Serum CTX for resorption and serum P1NP for formation. C-telopeptide of type I collagen (CTX) is released when osteoclasts degrade collagen, so it reflects resorption.

Why is "Serum calcium for resorption and serum phosphate for formation" not the answer?

Serum calcium and phosphate are tightly regulated and are not sensitive markers of turnover.

Why is "Serum P1NP for resorption and serum CTX for formation" not the answer?

This reverses the markers: P1NP is a formation marker and CTX is a resorption marker.

Why is "Bone-specific alkaline phosphatase for resorption and urinary NTX for…" not the answer?

Bone-specific alkaline phosphatase is an osteoblast marker, and urinary NTX is a resorption marker, so both roles are reversed.

What concept does this question test?

It tests Metabolic bone disease: bone turnover markers in Orthopaedics. Procollagen type I N-terminal propeptide (P1NP) and bone-specific alkaline phosphatase and osteocalcin come from osteoblasts and reflect formation. Antiresorptive drugs such as bisphosphonates lower CTX quickly.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Metabolic bone disease: bone turnover markers?

Pair each fracture with its classic complication and nerve injured. Then use the flashcards and the other Orthopaedics questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.