Coagulation Disorders USMLE Step 1 Practice Question
A 68-year-old man with newly diagnosed gastric cancer presents with acute-onset bilateral lower extremity pain and swelling. Vital signs show BP 138/82, HR 92, RR 18, temp 37.2°C, SpO2 98% on room air. Examination reveals bilateral calf erythema and tenderness. D-dimer is markedly elevated at 8.5 μg/mL; compression ultrasound confirms bilateral DVTs. He denies recent immobilization, surgery, or trauma. Platelet count is normal. Which of the following best explains the underlying mechanism for these thrombotic complications?
Answer choices
- ASurgical manipulation increasing endothelial damage
- BProtein C resistance from factor V Leiden
- CImmobilization causing venous stasis
- DCancer-induced tissue factor expression activating the extrinsic coagulation pathwayCorrect answer
- EAntithrombin deficiency from hepatic dysfunction
- FPlatelet aggregation from circulating immune complexes deposited on vessel walls
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