Which pattern of thyroid function tests is typical in autoimmune Hashimoto thyroiditis?

• A. Normal TSH with normal T4
• B. Elevated TSH with low T4 and T3
• C. Low TSH with high T4
• D. Elevated TSH with high T4

Answer: (B)

Hashimoto thyroiditis causes autoimmune destruction of the thyroid gland, leading to primary hypothyroidism. When the gland can't produce enough thyroid hormone, the pituitary steps up TSH production in an attempt to stimulate the thyroid, so TSH becomes elevated while free T4 and T3 fall. This pattern—high TSH with low T4 (and T3)—is typical for Hashimoto’s. If TSH were normal with normal T4, the patient would be euthyroid, not affected by Hashimoto’s. Elevated TSH with high T4 or low TSH with high T4 would indicate hyperthyroidism or a different pituitary/thyroid issue, not autoimmune Hashimoto’s.