Coagulation Disorders USMLE Step 1 Practice Question
A 45-year-old woman undergoes preoperative screening before elective surgery. Laboratory studies reveal elevated aPTT (48 seconds) with normal PT (12 seconds), platelet count (245,000/μL), and fibrinogen (340 mg/dL). Mixing study with normal plasma shows persistent aPTT prolongation. She denies personal or family history of bleeding and takes no anticoagulants. Vital signs are stable: BP 128/82 mmHg, HR 76/min, RR 14/min, Temp 37°C. Which of the following is the most likely explanation?
Answer choices
- AFactor XII deficiency
- BHeparin contamination of sample
- CLupus anticoagulantCorrect answer
- DFactor V deficiency
- Evon Willebrand disease
- FFactor VIII deficiency
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