Antitriiodothyronine antibody in patient with Hashimoto's thyroiditis.

We described a 44-year-old female patient with a history of goiter for 2 months. Physical examination revealed a diffusely enlarged thyroid gland weighing 40 g firm to hard in consistency. She was clinically euthyroid and had neither ophthalmopathy nor dermopathy. Serum thyroid hormone levels revealed total T4 (RIA) of 4.8 micrograms/dL (normal, 4-11 micrograms/dL), total T3 (RIA) of above 600 ng/dL (70-175 ng/dL), and TSH (IRMA) of 54 mU/L (0.3-6 mU/L). Antithyroglobulin and antiperoxidase antibody titers were 1:5,120 and 1:409,260, respectively. Because of the discrepancy between the patient's clinical status and laboratory values, assay for thyroid hormone autoantibodies (THAA) was done and subsequently demonstrated antitriiodothyronine antibody with percentage of precipitation by polyethylene of 98.4 per cent (normal range, 3.06 +/- 8.58%). In conclusion, THAA should be suspected in patients whose clinical status is incoherent with the thyroid function test.