Coagulation Disorders USMLE Step 1 Practice Question
A 72-year-old man hospitalized for cholangitis treated with broad-spectrum antibiotics for 10 days develops spontaneous gum bleeding and ecchymoses. Vital signs: BP 128/76, HR 92, RR 16, Temp 37.2°C, SpO2 98%. Laboratory studies reveal PT 18.2 seconds (normal 12-13), PTT 38 seconds (mildly prolonged), platelet count 245,000/μL, and INR 1.8. Prothrombin time corrects with fresh frozen plasma. Stool guaiac is negative. Which mechanism best explains these findings?
Answer choices
- AAutoantibody-mediated inhibition of ADAMTS13
- BConsumption of coagulation factors by widespread microthrombi
- CReduced gamma-carboxylation of coagulation factors II, VII, IX, and XCorrect answer
- DDefective platelet adhesion due to absent GpIb
- EImmune destruction of platelets by anti-GpIIb/IIIa antibodies
- FImpaired hepatic synthesis of fibrinogen and factor V due to acute liver dysfunction
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