Abstract: Objective  To study the value of  iodine uptake rate of thyroid in evaluating the timing of withdrawal of Graves   hyperthyroidism after treatment with methimazole. Methods  Fortyeight cases of  Graves  hyperthyroidism were treated regularly by methimazole for two years from March 2015 to April 2018, the symptoms of hyperthyroidism disappeared, serum free triiodothyronine(FT3), free thyroxine(FT4), super sensitivity thyroid stimulating hormone(sTSH) and thyrotropin prceptor antibody(TRAb)  levels returned to normal. 24 hours iodine uptake rate of thyroid of all cases were tested suspension of drugs after five days. The cases were divided into two groups according to the results of 24 hours iodine intake rate, iodine 131 intake normal group and elevated group. 15 cases (15/48) of intake iodine131 normal group stopped taking antihyperthyroidism drug at the same time. 33 cases(33/48) of intake iodine131 the elevated group were divided into the discontinuation group and the medication group, 12 cases(12/33)  of the medication group continued antihyperthyroidism drugs until the normal rate of iodine intake. 21 cases(21/33)  of the drug withdrawal group were stopped taking antihyperthyroidism drugs. Two groups of cases were followed up after nine months, the recurrence rate of hyperthyroidism was observed and the risk factors of recurrence were analyzed in two groups. Results   There were 5 cases (5/15) of recurrence of hyperthyroidism in iodine131 intake normal group, There were 3 cases(3/12)  of recurrence of hyperthyroidism in medication group, There were 8 cases (8/27) of recurrence in two groups. 17 cases(17/21) were recurrence of hyperthyroidism in discontinuation group. The recurrence case of hyperthyroidism in discontinuation group was higher than  iodine 131 intake normal group and  medication group altogether. Comparison of recurrence rate of hyperthyroidism between iodine131 normal group and medication group, the recurrence rate of hyperthyroidism in two groups was statistically significant (P<0.05). The risk factors of recurrence included strong positive of TRAb, grade Ⅲ goiter, increased iodine uptake rate of thyroid of 24 hours and less than 25 years old. Conclusion   The 24 hours iodine uptake rate of thyroid was valuable for evaluating the timing of Graves  hyperthyroidism after methimazole treatment; The timing of withdrawal of methimazole after Graves  hyperthyroidism being treated with methimazole should consider all aspects. In addition to the disappearance of symptoms and signs of hyperthyroidism, FT3, FT4, sTSH, TRAb and 24hours iodine uptake rate of thyroid should be detected, it can reduce the recurrence rate of Graves   hyperthyroidism combinating of the three after methimazole treated.

Key words: hyperthyroidism, methimazole, iodine