Which diagnostic study is most appropriate to confirm autoimmune thyroiditis in a postpartum patient?

• A. Radioactive iodine uptake
• B. Computed tomography
• C. Magnetic resonance imaging
• D. Thyroid-stimulating hormone

Answer: (A)

In postpartum autoimmune thyroiditis, inflammation damages the thyroid tissue and reduces its ability to take up iodine. A radioactive iodine uptake scan measures how much iodine the thyroid absorbs; in autoimmune thyroiditis this uptake is decreased, helping distinguish it from other causes of thyrotoxicosis (like Graves disease, which shows increased uptake). Structural imaging with CT or MRI won’t reveal autoimmune inflammation of the thyroid, and measuring TSH shows thyroid function but doesn’t confirm autoimmune etiology. Therefore, the radioactive iodine uptake test is the most informative option for confirming autoimmune thyroiditis in this setting.