Review Question - QID 210599

A 70-year-old man presents to his primary care physician for a general checkup. He states that he has been doing well and taking his medications as prescribed. He recently started a new diet and supplement to improve his health and has started exercising. The patient has a past medical history of diabetes, myocardial infarction, and hypertension. He denies any shortness of breath at rest or with exertion. His temperature is 98.7°F (37°C), blood pressure is 137/88 mmHg, pulse is 78/min, respirations are 15/min, and oxygen saturation is 99% on room air. An ECG is performed and is within normal limits. Laboratory values are ordered as seen below.

Serum:
Na+: 139 mEq/L
Cl-: 100 mEq/L
K+: 6.7 mEq/L
HCO3-: 25 mEq/L
Glucose: 133 mg/dL
Ca2+: 10.2 mg/dL

Which of the following is the most likely cause of this patient's presentation?