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Protein C Deficiency — RACP Adult Medicine MCQ

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ModerateHaematologyProtein C DeficiencyRACP Adult Medicine

A 35-year-old woman presents with recurrent deep vein thromboses. She has a family history of VTE. Thrombophilia testing performed 3 months after completing anticoagulation shows protein C level of 35% (normal 70–140%). What is the recommended duration of anticoagulation?

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Correct answer: E — Lifelong

Protein C deficiency (particularly levels <50%) with recurrent VTE is an indication for lifelong anticoagulation given the high recurrence risk. Protein C, protein S, and antithrombin levels should be tested at least 2–4 weeks after completing anticoagulation and NOT during acute thrombosis or on anticoagulants (which affect levels). Warfarin reduces protein C levels, so testing should be off warfarin.

Reference: eTG – 2025 – Haematology; ISTH – 2023 – Thrombophilia Testing Guidelines