Review Question - QID 216611

A 72-year-old man presents to his primary care physician for a general checkup. He states that he has been a bit more fatigued lately but believes it is secondary to poor sleep at his new house. The patient is otherwise healthy and takes no medications. His temperature is 98.0°F (36.7°C), blood pressure is 141/90 mmHg, pulse is 82/min, respirations are 16/min, and oxygen saturation is 98% on room air. Physical exam is notable only for minor pallor but is otherwise unremarkable. Basic laboratory studies are ordered as seen below.

Hemoglobin: 10 g/dL
Hematocrit: 30%
Leukocyte count: 67,500/mm^3
Platelet count: 119,000/mm^3

Serum:
Na: 141 mEq/L
Cl: 103 mEq/L
K: 4.0 Eq/L
HCO3-: 24 mEq/L
BUN: 22 mg/dL
Glucose: 109 mg/dL
Creatinine: 1.2 mg/dL
Ca: 10.0 mg/dL

Which of the following is the most likely diagnosis?