Review Question - QID 108700

A 72-year-old man presents to his primary care provider for fatigue. He has been so tired recently that he has struggled to get out of bed in the morning, and he has been calling out sick from work. He denies any changes in sleep but endorses a depressed mood since his wife died 6 months ago. He has struggled to take on the household tasks that she used to manage. He has a medical history of hypertension, hyperlipidemia, chronic pancreatitis, and osteoarthritis for which he takes amlodipine, atorvastatin, and diclofenac gel. He had a positive tuberculin skin test on routine screening last year, for which he completed 9 months of treatment with isoniazid. He does not smoke cigarettes. He rarely exercises and eats a diet of mostly canned foods. His temperature is 97.2°F (36.2°C), blood pressure is 156/97 mmHg, pulse is 78/min, and respirations are 12/min. On physical exam, he appears older than his stated age and has conjunctival pallor. He has poor dentition and is wearing dentures. Sensation is intact to light touch in all extremities. Laboratory tests reveal the following:

Leukocyte count: 6,800/mm^3
Hemoglobin: 9.2 g/dL
Hematocrit: 29%
Mean corpuscular volume: 110 µm^3
Platelet count: 208,000/mm^3

A peripheral smear is performed and can be seen in Figure A. Which of the following is the most likely risk factor for this patient's condition?