Abstract:Objective To observe the incidence of permanent hypothyroidism at different thyroid stimulating hormone (TSH) levels maintained by levothyroxine sodium (Jiaheng) replacement therapy in early-onset hypothyroidism patients with Graves′ disease (GD) treated with iodine-131(¹³¹I) for 3 months. Methods Seventy patients diagnosed as hypothyroidism by rechecking thyroid function 3 months after ¹³¹I treatment because of GD were randomly divided into group A in which alternative therapy was given with TSH at normal level about 0. 27-4. 2 mIU/L and group B in which alternative therapy was given with TSH at normal and slightly higher levels about 4. 2-10 mIU/L(n=35, each). The incidence of permanent hypothyroidism was observed by determination of thyroid function after treatment with ¹³¹I for one year. Results After treatment with ¹³¹I for one year, the incidence of permanent hypothyroidism was 88. 6% in group A and 65. 7% in group B(χ²=5.185, P<0.05). Conclusion In early-onset hypothyroidism patients with GD treated with ¹³¹I for 3 months, the incidence of permanent hypothyroidism can be reduced significantly by using levothyroxine sodium replacement therapy to keep TSH at a slightly higher level.