A 40 year old female came to your OPD with complaints of excessive fatigue, constipation, alopecia & gives history of weight gain of around 5 kg in last 3 months despite regular diet & physical activity. Her thyroid profile show TSH- 20 mU/L & free T4 is low. Your next step in diagnosis of etiology would be?
Antithyroid peroxidase antibody Antithyroglobulin antibody Radioiodine uptake scan Thyroid ultrasound