Review Question - QID 210563

A 17-year-old girl is brought to her pediatrician by her mother for a wellness checkup. The patient is doing well in school and has no concerns. She has a medical history of anxiety and is currently taking clonazepam as needed. Her family history is remarkable for hypertension in her mother and father and renal disease in her grandparents and aunt. Her temperature is 98.6°F (37.0°C), blood pressure is 97/68 mmHg, pulse is 90/min, respirations are 11/min, and oxygen saturation is 99% on room air. The patient's BMI is 23 kg/m^2. Cardiac, pulmonary, and neurological exams are within normal limits. Laboratory values are ordered as seen below.

Hemoglobin: 10 g/dL
Hematocrit: 29%
Leukocyte count: 6,500/mm^3 with normal differential
Platelet count: 190,000/mm^3

Serum:
Na+: 137 mEq/L
Cl-: 97 mEq/L
K+: 3.5 mEq/L
HCO3-: 29 mEq/L
BUN: 20 mg/dL
Glucose: 67 mg/dL
Creatinine: 1.1 mg/dL
Ca2+: 10.2 mg/dL

Urine:
pH: 4.5
Color: yellow
Glucose: none
Chloride: 4 mEq/L
Sodium: 11 mEq/L

Which of the following is the most likely diagnosis?