Clinical biochemistry: bone turnover markers: practice question

A Biochemistry 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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Biochemistry · Clinical biochemistry: bone turnover markers

Sample item

A postmenopausal woman is monitored on a bisphosphonate. Which of the following is a marker of bone resorption rather than bone formation?

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

The answer and the reasoning

B. Serum C-terminal telopeptide of type I collagen (CTX)

CTX is released when osteoclasts degrade type I collagen, so it measures resorption and falls rapidly with antiresorptive therapy. P1NP, osteocalcin and bone-specific ALP are products of osteoblasts and indicate bone formation. Urinary deoxypyridinoline is another resorption marker.

Option by option

  • A. Bone-specific alkaline phosphatase

    Bone-specific alkaline phosphatase is an osteoblast enzyme and reflects formation.

  • B. Serum C-terminal telopeptide of type I collagen (CTX) (correct)

    Correct. CTX is a collagen breakdown product released during osteoclastic resorption.

  • C. Procollagen type I N-terminal propeptide (P1NP)

    P1NP is the propeptide released during type I collagen synthesis, so it marks formation.

  • D. Serum osteocalcin

    Osteocalcin is made by osteoblasts and is a formation marker.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Serum C-terminal telopeptide of type I collagen (CTX). CTX is released when osteoclasts degrade type I collagen, so it measures resorption and falls rapidly with antiresorptive therapy.

Why is "Bone-specific alkaline phosphatase" not the answer?

Bone-specific alkaline phosphatase is an osteoblast enzyme and reflects formation.

Why is "Procollagen type I N-terminal propeptide (P1NP)" not the answer?

P1NP is the propeptide released during type I collagen synthesis, so it marks formation.

Why is "Serum osteocalcin" not the answer?

Osteocalcin is made by osteoblasts and is a formation marker.

What concept does this question test?

It tests Clinical biochemistry: bone turnover markers in Biochemistry. P1NP, osteocalcin and bone-specific ALP are products of osteoblasts and indicate bone formation. Urinary deoxypyridinoline is another resorption marker.

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 Clinical biochemistry: bone turnover markers?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.