Haemostasis: D-dimer: practice question

A Physiology 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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Physiology · Haemostasis: D-dimer

Sample item

A patient with severe sepsis has platelets 40,000/uL, prolonged PT and aPTT, low fibrinogen and a markedly raised D-dimer. Why does D-dimer rise in this condition?

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

The answer and the reasoning

B. Plasmin degrades fibrin that thrombin has formed and factor XIIIa has cross-linked

D-dimer is a fragment of fibrin that has been cross-linked by factor XIIIa and then digested by plasmin. A raised level therefore shows that thrombin generated fibrin and the fibrinolytic system acted on it, as in DIC. Fibrinogen digestion alone, as in primary fibrinolysis, yields fragments but little D-dimer.

Option by option

  • A. Antithrombin is consumed, releasing D-dimer from platelets

    Antithrombin consumption does not release D-dimer, which is derived from fibrin.

  • B. Plasmin degrades fibrin that thrombin has formed and factor XIIIa has cross-linked (correct)

    Correct. D-dimer marks lysis of cross-linked fibrin, which needs thrombin activity.

  • C. Plasmin degrades circulating fibrinogen that is not yet converted to fibrin

    Plasmin acting on fibrinogen produces fibrinogen degradation products without cross-linked D-dimer.

  • D. Activated protein C cleaves fibrinogen into D-dimer fragments

    Activated protein C inactivates factors Va and VIIIa and does not cleave fibrinogen.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, Plasmin degrades fibrin that thrombin has formed and factor XIIIa has cross-linked. D-dimer is a fragment of fibrin that has been cross-linked by factor XIIIa and then digested by plasmin.

Why is "Antithrombin is consumed, releasing D-dimer from platelets" not the answer?

Antithrombin consumption does not release D-dimer, which is derived from fibrin.

Why is "Plasmin degrades circulating fibrinogen that is not yet converted to…" not the answer?

Plasmin acting on fibrinogen produces fibrinogen degradation products without cross-linked D-dimer.

Why is "Activated protein C cleaves fibrinogen into D-dimer fragments" not the answer?

Activated protein C inactivates factors Va and VIIIa and does not cleave fibrinogen.

What concept does this question test?

It tests Haemostasis: D-dimer in Physiology. A raised level therefore shows that thrombin generated fibrin and the fibrinolytic system acted on it, as in DIC. Fibrinogen digestion alone, as in primary fibrinolysis, yields fragments but little D-dimer.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Haemostasis: D-dimer?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.