Q. A 62-year-old woman presents to the emergency department complaining of increasing pain and swelling in her left lower leg, which began suddenly two days ago. She reports a recent long-distance trip by plane 1 week prior and describes her occupation as an office administrator, primarily involving sedentary work. She denies any recent injuries but mentions a history of oral contraceptive use. She also has a history of occasional smoking. On examination, the left calf is visibly swollen and warm compared to the right calf. There is tenderness on deep palpation. Homans' sign is positive, and the circumference of the left calf is 3 cm larger than the right. Her vitals show a blood pressure of 120/80 mmHg, a heart rate of 98 beats per minute, a respiratory rate of 18 breaths per minute, and an oxygen saturation of 97% on room air. The lab investigations reveal a D-dimer level of 0.7 µg/mL, CBC shows a WBC count of 11,000 /µL, and normal platelet count and hemoglobin levels. The patient's coagulation profile shows a PT-INR of 1.2. What is the next best step in the management of this patient?