A 43-year-old woman presents with a 2-cm thyroid nodule discovered on palpation. She denies dysphagia, dyspnea, or neck pain. Vital signs: BP 128/82, HR 88, RR 16, Temp 37°C, SpO2 98%. Laboratory studies reveal suppressed TSH at 0.2 mIU/L (normal 0.4–4.0) with normal free T4. Thyroid ultrasound shows a solid, hypoechoic nodule without cystic features. She takes no thyroid medications. Which of the following is the best next step in evaluation?

1. A)Radioactive iodine uptake scanGABARITO
2. B)Measure anti-thyroid peroxidase antibodies
3. C)Water deprivation test
4. D)ACTH stimulation test
5. E)Immediate total thyroidectomy