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Vitamin K Dependent Factors — FRCA Primary MCQ

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HardPhysiology - Gastrointestinal & HepaticVitamin K Dependent FactorsFRCA Primary

Warfarin therapy is started without parenteral bridging in a patient at high thrombotic risk. Which early change best explains the potential transient prothrombotic state?

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Correct answer: B — Protein C activity falls before substantial reduction in procoagulant factor II activity

The best answer is “Protein C activity falls before substantial reduction in procoagulant factor II activity”. Warfarin reduces gamma-carboxylation of vitamin-K-dependent procoagulant factors and protein C together with protein S. Protein C has a relatively short half-life, so anticoagulant activity can decline early before the longer-lived procoagulant factor II falls sufficiently, creating transient hypercoagulability. It does not inhibit platelets or directly lower fibrinogen.

Reference: RCoA, Primary FRCA syllabus: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf; Hemostatic balance in acute liver failure: https://pmc.ncbi.nlm.nih.gov/articles/PMC7786276/