Approach to hypercoagulable disorders Quiz: Ace Your Exams

A 43-year-old man presents to the emergency department due to bilateral leg swelling. Three days ago, the patient developed a dull, achy pain and swelling in both calves. The swelling and pain have continued to worsen. The patient has had three lower extremity, and one upper extremity deep vein thromboses in the past. He does not currently take any medication. The patient does not use alcohol or tobacco, and he works as a waiter in a local restaurant. Temperature is 37.3 ºC (99.1 ºF), pulse is 84/min, respiratory rate is 18/min and blood pressure is 141/86 mmHg. On physical examination, both legs are edematous with mild erythema and tenderness to palpation. Lower extremity venous ultrasound with Doppler shows bilateral deep vein thromboses below the knee. The patient is given a dose of subcutaneous enoxaparin. Bloodwork is subsequently obtained. Which of the following tests is most appropriate to perform as part of the workup?