A 43 year old man presents to the emergency department complaining of a mildly swollen, painful leg for the past four days. He has felt well otherwise and has no fever, nausea, vomiting, shortness of breath, or chest pain. He denies any history of cancer, clotting disorders, trauma to the extremity, or previous thromboembolic disease. He has been commuting frequently to a neighboring city on business for the last two weeks. He has no significant past medical history and takes no medications. He is a ten-pack-year smoker but denies the use of drugs or alcohol. He lives locally with his family and has been with the same job for 15 years.

Physical exam reveals a well-developed and well-nourished male in no distress. He is experiencing mild pain. Vital signs are blood pressure 132/81, pulse 84, respirations 22, and temperature 37°C (98.6°F). Pulse oximetry reveals a room air oxygen saturation of 97%. His neck exam reveals no jugular venous distention and no bruits. Heart sounds are normal without murmur, gallop, or rub. Respirations are unlabored and without rales, wheezes or rhonchi. His abdominal exam is benign. His pulses are full and symmetric. His right calf is swollen three centimeters larger than his left, has very minimal erythema and is not warm, and is tender to palpation. No cords are palpable, but Homan's sign is positive.

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