Haematology: antithrombin deficiency: practice question

A Pathology 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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Pathology · Haematology: antithrombin deficiency

Sample item

A 28-year-old man has had two episodes of deep vein thrombosis, one in an unusual mesenteric vein. During treatment with intravenous unfractionated heparin, the aPTT stays near baseline even at high doses. Which inherited defect is most likely?

AAntithrombin deficiencyBProtein S deficiencyCFactor V LeidenDProthrombin G20210A variant

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

The answer and the reasoning

A. Antithrombin deficiency

Heparin acts by enhancing the activity of antithrombin, so patients with antithrombin deficiency show heparin resistance. It is autosomal dominant and carries a high risk of venous thrombosis.

Option by option

A. Antithrombin deficiency (correct)
Correct. Without adequate antithrombin, heparin cannot prolong the aPTT, giving heparin resistance.
B. Protein S deficiency
Protein S deficiency raises thrombosis risk through the protein C pathway without heparin resistance.
C. Factor V Leiden
Factor V Leiden causes activated protein C resistance but does not impair the heparin response.
D. Prothrombin G20210A variant
The prothrombin G20210A variant raises prothrombin level and thrombosis risk but not heparin resistance.

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.

Questions about this Pathology question

What is the answer to this Pathology question?

The best answer is A, Antithrombin deficiency. Heparin acts by enhancing the activity of antithrombin, so patients with antithrombin deficiency show heparin resistance.

Why is "Protein S deficiency" not the answer?

Protein S deficiency raises thrombosis risk through the protein C pathway without heparin resistance.

Why is "Factor V Leiden" not the answer?

Factor V Leiden causes activated protein C resistance but does not impair the heparin response.

Why is "Prothrombin G20210A variant" not the answer?

The prothrombin G20210A variant raises prothrombin level and thrombosis risk but not heparin resistance.

What concept does this question test?

It tests Haematology: antithrombin deficiency in Pathology. It is autosomal dominant and carries a high risk of venous thrombosis.

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 Haematology: antithrombin deficiency?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.