What is the most likely cause for this patient anemia

50 year old male complains of weakness and exertional shortness of breath. He denies any chest pain. He golfs twice a week and runs two miles every other day but the runs have been cut short secondary to his presenting symptoms. Vtal signs: BP=130/70mmHg,HR=98, RR=18. Physical exam is significant for pallor and a soft systolic murmur. Chest is clear to auscultation and there is no evidence of lower extremities edema.(Hint:shortness of breath in the absence of heart and lung pathilogies-think hematology.)
Which test would you order? why?

The patient returns four weeks later. Laboratory values are significant for a hemoglobin and hematocrit( H&H) of 10/32, reticular index of 2, low iron, and high total iron binding capacity (TIBC). What is the most appropriate next step in management?

What is the most likely cause for this patient’s anemia?