mrcgp akt MCQ (SBA): Hyperthyroidism (Graves' Disease)

A 40-year-old woman presents with a 6-month history of anxiety, palpitations, weight loss despite increased appetite, and heat intolerance. On examination, she has a fine tremor, warm peripheries, and a resting heart rate of 110 bpm. Thyroid examination reveals a symmetrically enlarged, non-tender goitre with an audible bruit. What investigation result would be most consistent with the suspected diagnosis?