Blood and immunity: activated protein C resistance: 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 · Blood and immunity: activated protein C resistance

Sample item

A 28-year-old woman has a deep vein thrombosis during pregnancy. PT and aPTT are normal, and protein C, protein S and antithrombin levels are normal, but the aPTT does not prolong when activated protein C is added. What is the likely basis?

AOverproduction of prothrombin from a gene variantBA mutant factor V that activated protein C cannot inactivateCDeficient antithrombin, so thrombin is not neutralisedDReduced protein S, the cofactor for protein C

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

The answer and the reasoning

B. A mutant factor V that activated protein C cannot inactivate

In factor V Leiden, an arginine substitution removes a cleavage site, so activated factor V persists after activated protein C acts. This produces resistance to activated protein C and a prothrombotic state, and it is the commonest inherited thrombophilia. Normal protein C, S and antithrombin levels exclude their deficiencies.

Option by option

A. Overproduction of prothrombin from a gene variant
A prothrombin gene variant raises prothrombin but would not produce resistance to activated protein C.
B. A mutant factor V that activated protein C cannot inactivate (correct)
Correct. Factor Va that resists cleavage keeps generating thrombin.
C. Deficient antithrombin, so thrombin is not neutralised
Antithrombin levels were stated to be normal.
D. Reduced protein S, the cofactor for protein C
Protein S levels were stated to be normal.

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 Physiology question

What is the answer to this Physiology question?

The best answer is B, A mutant factor V that activated protein C cannot inactivate. In factor V Leiden, an arginine substitution removes a cleavage site, so activated factor V persists after activated protein C acts.

Why is "Overproduction of prothrombin from a gene variant" not the answer?

A prothrombin gene variant raises prothrombin but would not produce resistance to activated protein C.

Why is "Deficient antithrombin, so thrombin is not neutralised" not the answer?

Antithrombin levels were stated to be normal.

Why is "Reduced protein S, the cofactor for protein C" not the answer?

Protein S levels were stated to be normal.

What concept does this question test?

It tests Blood and immunity: activated protein C resistance in Physiology. This produces resistance to activated protein C and a prothrombotic state, and it is the commonest inherited thrombophilia. Normal protein C, S and antithrombin levels exclude their deficiencies.

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 Blood and immunity: activated protein C resistance?

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.