A 50-year-old man with 4 weeks history of persistent documented fever and fatigue. He is known to have aortic stenosis with no other comorbidities. Examination reveals Temp 38.10C, BP 120/70mmHg. He has grade 4/6 ejection systolic murmur over the right sternal border. Laboratory evaluation reveals microcytic anemia and elevated ESR. Which of the following is the most appropriate test in diagnosing this patient?