Review Question - QID 108703

A 25-year-old woman presents to clinic with a 3-month history of frequent, loose stools and abdominal pain. She currently has 3-4 bowel movements per day, and she believes these episodes have been getting worse. She experiences occasional palpitations over the past few months as well. She denies fevers, chills, headache, blurry vision, cough, shortness of breath, wheezing, nausea, or vomiting. She describes her mood as irritable and she has been sleeping poorly. She has a history of asthma for which she uses an albuterol inhaler as needed. She also takes an oral contraceptive. She has not traveled recently and is a non-smoker. Her temperature is 98.6°F (37°C), pulse is 104/min, blood pressure is 95/65 mmHg, respirations are 16/min, and oxygen saturation is 99% on room air. She has unintentionally lost 6 pounds over a 1 month period. On physical exam, her thyroid gland appears symmetrically enlarged but is non-tender to palpation. There is an audible thyroid bruit. Ocular exam reveals exophthalmos. Her abdomen is soft and non-tender. Deep tendon reflexes are 3+ throughout. Lab results are as follows:

Serum:
Na+: 140 mEq/L
K+: 4.1 mEq/L
Cl-: 104 mEq/L
HCO3-: 26 mEql/L
Blood urea nitrogen: 18 mg/dL
Creatinine 0.9 mg/dL

Hemoglobin: 14.0 g/dL
Leukocyte count: 7,400/mm^3
Platelet count: 450,000/mm^3

A urine pregnancy test is negative. The patient is started on a medication for symptomatic relief. Which of the following is the most appropriate next step in management?