Thyroid hormone autoantibodies in a case of Hashimoto's disease.

A case of Hashimoto's disease is reported. The serum contained antibodies binding T3 and T4. The binding capacity and affinity constants for T3 were 0.03 mumol/l and 3.4 x 10(9) l/mol and for T4 0.3 mumol/l and 1.4 x 10(9) l/mol, respectively. After total thyroid lobectomy on the left and subtotal on the right the autoantibodies disappeared from the serum. Thyroid tissue from the patient proved to contain an antithyroglobulin. According to the findings, the T3- and T4-binding antibodies are directed against thyroglobulin. It is of clinical importance to bear these autoantibodies in mind as possible errors in measuring T3 and T4 by radioimmunoassay (RIA). If RIA determination gives unexpectedly high or low T3 and/or T4 values, testing of non-specific binding is recommended.