<prompt> 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 mUL free T4 is low. Your next step in diagnosis of etiology would be?Antithyroid peroxidase antibodyAntithyroglobulin antibodyRadioiodine uptake scanThyroid ultrasound  <response>: The most common cause of hypothyroidism in India is Hashimoto thyroiditis Since TSH levels are elevated in this patient, we will suspect primary cause of hypothyroidism. Therefore, Anti peroxidase antibody test is useful If TSH level is low then we suspect secondary cause pituitary and go for MRI head Antithyroglobulin antibodies- found in Hashimotos disease Thyroid ultrasound- useful for presumed multinodular goiter Radioiodine uptake scan- will not be useful 