Objective To analyze the characteristics of thyroid function change at 1st, 3rd and 6th months after ¹³¹I treatment of Graves' hyperthyroidism and determine the correlation between level of antibodies before treatment and prognosis.

Methods A prospective study was conducted in 80 patients with Graves' hyperthyroidism patients treated with ¹³¹I for the first time from March 2016 to May 2016 in the First Hospital of China Medical University. The patients consisted of 20 males and 60 females,with median age of 19−70 (40.5±12.8) years. The patients were followed up and reexamined at 1st, 3rd, and 6th months after treatment. According to the thyroid function change, the patients at 1st and 3rd months were separately divided into four groups (thyroid function increased, thyroid function improved, thyroid function normal and thyroid function decreased). Patients at 6th month were divided into four groups, including improved completely, improved partially, invalid (these 3 groups are called non-hypothyroidism group) and hypothyroidism. The cured group including improved completely and the hypothyroidism, and the non-cured group including the improved partially, invalid and the patients who have secondary treatment.The characteristics of thyroid function change at 1st, 3rd, and 6th months were reviewed, and the correlation between level of antibodies (anti thyroglobulin antibodies (TgAb), thyroid peroxidase antibody (TPOAb) and thyrotrophin receptor antibody (TRAb)) and prognosis was found. Chi-square test was used to compare the differences in the incidence of hypothyroidism at 3rd month between each group at 1st month. Kappa test was used to analyze the consistency between changes in thyroid function at 3rd month and the curative effect at 6th month. The relationship between antibody level before treatment and the curative effect was analyzed by Wilcoxon test.

Results The incidence of hypothyroidism at 3rd month significant differed between thyroid function increased (15.00(3/20)) and “normal and thyroid function decreased” (including thyroid function normal and thyroid function decreased) (88.90% (8/9)) at 1st month (χ²=14.39, P<0.01). The incidence of hypothyroidism at 3rd month significantly differed between thyroid function improved (25.49% (3/51)) and “normal and thyroid function decreased” at 1st month (χ²=13.52, P<0.01). The incidence of hypothyroidism at 3rd month between thyroid function increased and thyroid function improved at 1st month had no statistical difference (χ²=0.91, P>0.05). The consistency analysis showed that the Kappa value was 0.812 in comparison between thyroid function decreased at 3rd month and hypothyroidism at 6th month (P<0.01).The Kappa value was 0.615 in comparison between thyroid function normal at 3rd month and improved completely at 6th month (P<0.01). The Kappa value was 0.519 in comparison between thyroid function improved at 3rd month and improved partially at 6th month (P<0.01). The levels of TgAb51.53 (9.05, 781.19) U/mL vs.14.30 (3.33, 45.14) U/mL and TPOAb577.50 (197.89, 1000) U/mL vs.397.71 (98.41, 955.68) U/mL before treatment between hypothyroidism and non-hypothyroidism at 6th month had no significant differences (u=249.00, 306.50, both P>0.05). The level of TRAb11.43 (4.34, 32.42) IU/L vs.19.82 (7.95, 39.14) IU/L before treatment in cure group and non-cure group at 6th month had significant differences (u=557.50, P<0.05).

Conclusions The clinical outcome at 6th month after ¹³¹I treatment can be evaluated and predicted by closely observing the change trend of thyroid function at 1st and 3rd month after ¹³¹I treatment. There was no correlation between the level of TgAb and TPOAb before treatment and occurrence of hypothyroidism, and there was correlation between the level of TRAb before treatment and the cure of hyperthyrodism, and it had significant difference.