[False radioimmuno-assay of thyroxine and triiodothyronine in the presence of hormone-binding autoantibodies in serum (author's transl)].

Radioimmunoassay of thyroxine and triiodothyronine in a 14-year-old girl with primary hypothyroidism and nodular goitre as a result of Hashimoto's thyroiditis gave falsely low values due to the presence of hormone-binding antibodies. Such antibodies occur in Hashimoto's thyroiditis and thyroid carcinoma. Their presence requires special methods for determining these hormones.