Review Question - QID 213630

A 41-year-old man presents to his primary care physician with a 3-month history of dyspnea on exertion. He says that he recently started playing in a father-son recreational soccer league and realized that he begins to become short of breath almost immediately after starting to play. He says that he was never the most physically active person and currently works as an office secretary. He says that he became worried because he feels like his level of fatigue and shortness of breath is unusual for someone of his age. Physical exam reveals splenomegaly but is otherwise unrevealing. A peripheral blood smear is obtained and the results are shown in Figure A. Which of the following would most likely reveal the etiology of this patient's symptoms?