Review Question - QID 109679

A 32-year-old woman presents to her primary care physician for recent onset headaches, weight loss, and restlessness. She has felt sweaty and generally uncomfortable. The patient’s medical history is unremarkable except for a recent viral respiratory infection which resolved on its own. The patient is not currently on any medications. Her temperature is 99.5°F (37.5°C), blood pressure is 127/68 mmHg, pulse is 110/min, respirations are 14/min, and oxygen saturation is 98% on room air. The patient is sweaty and uncomfortable with a rapid pulse. The patient demonstrates no abnormalities on HEENT exam. The patient’s laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 8,500/mm^3 with normal differential
Platelet count: 195,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 102 mEq/L
K+: 4.4 mEq/L
HCO3-: 24 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.0 mg/dL
Ca2+: 10.2 mg/dL
TSH: .03 mIU/L
AST: 12 U/L
ALT: 10 U/L

The patient is prescribed propranolol and propylthiouracil. She returns 1 week later complaining of fatigue. Laboratory values are ordered as seen below.

Hemoglobin: 12 g/dL
Hematocrit: 36%
Leukocyte count: 8,500/mm^3 with normal differential
Platelet count: 195,000/mm^3

Serum:
Na+: 139 mEq/L
Cl-: 102 mEq/L
K+: 4.4 mEq/L
HCO3-: 24 mEq/L
BUN: 20 mg/dL
Glucose: 99 mg/dL
Creatinine: 1.0 mg/dL
Ca2+: 10.2 mg/dL
TSH: 6.0 mIU/L
AST: 12 U/L
ALT: 10 U/L

Which of the following is the most appropriate next step in management?