ABSTRACT
Autoantibodies against thyroid hormones can be detected in the sera of patients with both thyroidal and non-thyroidal disorders. These antibodies interfere with the radioimmunoassay of serum total and free thyroid hormone concentrations, resulting in a discrepancy between the measured hormone levels and clinical features. This can in turn lead to an erroneous diagnosis and patients may receive unnecessary treatment from physicians who are unaware of the presence of the autoantibodies. We experienced a woman having Hashimotos' thyroiditis with a spurious elevation of total T3 and free T3 values according to one-step analog-tracer radioimmunoassay who was had been treated as Graves' disease in past. Through the use of a polyethylene glycol precipitation method, she was subsequently revealed to have anti-triiodothyronine autoantibodies. We report this case with a review of related literature.