Haemodynamics: 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 · Haemodynamics: antithrombin deficiency

Sample item

A 30-year-old woman with extensive iliofemoral thrombosis has an aPTT that barely rises despite escalating intravenous unfractionated heparin doses. Her father also had recurrent thromboses. Which deficiency best explains the heparin resistance?

AAntithrombinBProtein SCFactor XIIDPlasminogen

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

The answer and the reasoning

A. Antithrombin

Heparin acts by binding antithrombin and greatly enhancing its inhibition of thrombin and factor Xa. When antithrombin is inherited at low levels, heparin has little to potentiate, so the aPTT does not prolong and thrombosis recurs. Treatment may need antithrombin replacement or direct inhibitors.

Option by option

A. Antithrombin (correct)
Correct. Heparin needs antithrombin to work, so low levels cause resistance.
B. Protein S
Protein S deficiency causes thrombophilia but does not affect heparin response.
C. Factor XII
Factor XII deficiency prolongs aPTT without bleeding and is not a heparin target.
D. Plasminogen
Plasminogen deficiency impairs fibrinolysis and gives ligneous conjunctivitis, 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. Heparin acts by binding antithrombin and greatly enhancing its inhibition of thrombin and factor Xa.

Why is "Protein S" not the answer?

Protein S deficiency causes thrombophilia but does not affect heparin response.

Why is "Factor XII" not the answer?

Factor XII deficiency prolongs aPTT without bleeding and is not a heparin target.

Why is "Plasminogen" not the answer?

Plasminogen deficiency impairs fibrinolysis and gives ligneous conjunctivitis, not heparin resistance.

What concept does this question test?

It tests Haemodynamics: antithrombin deficiency in Pathology. When antithrombin is inherited at low levels, heparin has little to potentiate, so the aPTT does not prolong and thrombosis recurs. Treatment may need antithrombin replacement or direct inhibitors.

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 Haemodynamics: 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.