Serum thyrotropin-binding inhibiting immunoglobulin and thyroperoxidase antibody in Graves' hyperthyroidism after ¹³¹I therapy

Seventeen patients who received radioiodine (¹³¹I) therapy for Graves' hyperthyroidism had serial blood samples taken before therapy and after therapy for a period of at least 1 year. At 1 year post-therapy, six patients were hypothyroid. Seven patients were euthyroid, and four patients were hyperthyroid. Prior to isotope administration, 14 patients had detectable serum thyrotropin-binding inhibiting immunoglobulin (TBII) and 16 patients had detectable serum thyroperoxidase antibody (TPOAb). Three to 6 months after therapy, 11 of 14 TBII-positive patients demonstrated a marked increase (> 10%) in serum TBII activity. Four patients out of 11 developed hypothyroidism and six of the 11 developed euthyroidism. A decrease in TBII was observed in three patients who developed hyperthyroidism. In the three patients with undetectable TBII prior to therapy, two had high titers of TPOAb. Seven patients demonstrated a marked increase in TPOAb 3 to 6 months after therapy. Of these, four developed hypothyroidism and three developed euthyroidism, whereas three of the four patients who had a marked decrease in TPOAb developed hyperthyroidism. This study demonstrated that an increase in serum TBII and TPOAb activity 3 to 6 months after ¹³¹I therapy, may be useful in predicting which patients may develop euthyroidism or hypothyroidism after 1 year of ¹³¹ therapy.