Coagulation Disorders USMLE Step 1 Practice Question
A 66-year-old man hospitalized for pulmonary embolism is started on intravenous unfractionated heparin. On hospital day 6, he develops right leg pain and swelling. Vital signs show BP 138/82, HR 98, RR 18, temp 37.2°C, SpO2 98%. Laboratory studies reveal platelet count decreased from 240,000 to 82,000/mm³, with normal PT and aPTT. He denies recent surgery or trauma. Which of the following is the most likely mechanism underlying his clinical deterioration?
Answer choices
- AVitamin K depletion due to intestinal flora suppression
- BDirect toxic suppression of megakaryocytes by heparin
- CAntibodies against platelet factor 4 heparin complexes causing platelet activationCorrect answer
- DMechanical destruction of platelets in the spleen
- EInherited deficiency of antithrombin III
- FImmune complex deposition on platelet surfaces leading to complement-mediated lysis
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.