Review Question - QID 108995

A 45-year-old African American woman presents to her primary care physician for not feeling well. She states she has had a cough for the past week. She also has abdominal pain and trouble focusing that has been worsening and has lost 5 pounds recently. Her gastroesophageal reflux disease (GERD) has been poorly controlled recently. The patient is a non-smoker and has a history of GERD for which she takes antacids. Her temperature is 98.6°F (37°C), blood pressure is 115/71 mmHg, pulse is 72/min, and respirations are 12/min. A physical exam is within normal limits. Laboratory studies are ordered and are below:

Serum:
Na+: 139 mEq/L
K+: 4.1 mEq/L
Cl-: 101 mEq/L
HCO3-: 24 mEq/L
Urea nitrogen: 12 mg/dL
Glucose: 70 mg/dL
Creatinine: 0.9 mg/dL
Ca2+: 12.5 mg/dL
Alkaline phosphatase: 150 U/L
Phosphorus: 2.0 mg/dL

Urine:
Color: amber
Nitrites: negative
Sodium: 5 mmol/24 hours
Red blood cells: 0/hpf

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