A 62-year-old man arrives for his first checkup in 20 years. He is a smoker who received a diagnosis of hypertension many years ago, but did not take medication or return to his primary care...

A 62-year-old man arrives for his first checkup in 20 years. He is a smoker who received a diagnosis of hypertension many years ago, but did not take medication or return to his primary care physician. On physical examination, his blood pressure is 180/105 mm Hg. He is well-appearing but overweight. His laboratory examination is significant for sodium 138 mEq/L, potassium 5.8 mEq/L, chloride 104 mEq/L, bicarbonate 20 mEq/L, BUN 60 mg/dL,creatinine 2.8 mg/dL,and glucose of 230 mg/dL. What is the most likely cause of his decreased bicarbonate?

A. Diabetic ketoacidosis

B. Hypertension

C. Renal insufficiency

D. Diarrhea

E. Chronic obstructive pulmonary disease