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Heparin-induced thrombocytopenia — USMLE Step 3 MCQ

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HardInternal Medicine (chronic management)Heparin-induced thrombocytopeniaUSMLE Step 3

A 64-year-old hospitalized man receiving unfractionated heparin for pulmonary embolism develops new leg pain 7 days later. Platelet count has fallen from 240,000/mm3 to 92,000/mm3. Duplex ultrasonography shows a new femoral vein thrombosis. Which of the following is the most likely explanation for this patient's findings?

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Correct answer: A — Antibodies activating platelets through platelet factor 4-heparin complexes

HIT is an immune-mediated prothrombotic disorder caused by antibodies to platelet factor 4-heparin complexes that activate platelets.

Reference: American Society of Hematology HIT guideline