Review Question - QID 212662

A 60-year-old man presents to the emergency department for fatigue and feeling off for the past week. He has not had any sick contacts and states that he can’t think of any potential preceding symptoms or occurrence to explain his presentation. The patient has a past medical history of diabetes, hypertension, and congestive heart failure with preserved ejection fraction. His temperature is 98°F (36.7°C), blood pressure is 125/65 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 100% on room air. Laboratory values are obtained and shown below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 197,000/mm^3

Serum:
Na+: 147 mEq/L
Cl-: 105 mEq/L
K+: 4.1 mEq/L
HCO3-: 26 mEq/L
BUN: 21 mg/dL
Glucose: 100 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.1 mg/dL
AST: 12 U/L
ALT: 10 U/L

Urine:
Appearance: clear
Specific gravity: 1.003

The patient is admitted to the floor, a water deprivation test is performed, and his urine studies are repeated yet unchanged. Which of the following is the best next step in management?