 Introduction The aim of this study was to submit the ideal delay period of Carbimazole for hyperthyroidism patients using thyroid function test. It may be possible to perform thyroid scan with a minimum delay period of carbimazole, this can be time saving and decrease the adverse effects of discontinuing carbimazole.  Patients and Methods Among all the patients with hyperthyroidism who referred to nuclear medicine department of Khartoum Oncology Hospital, during the period between December 2018 and December 2019, 51 patients who were on Carbimazole were selected. A Thyroid Function Test (TFT) was obtained while they ware on medication for all these patients and then they were divided into three groups upon TFT results each with different Carbimazole delay period (A,B,C). We asked each group; to discontinue the usage Carbimazole for 3, 5 and 7 days respectively and then a second TFT was obtained. After that thyroid scan was performed for these patients. Revealed data was analyzed under supervision of statistical specialist with descriptive methods on SPSS.  Results 11 patients were males and the other 40 were females. Mean age of group A, B and C were 37 , 47 , 47 respectively. The mean of the first TFT (T3, T4 and TSH) for group A was: (5.2, 225.59, 0.17), group B: (5.28, 231.86, 0.13) and group C: (5.34, 246.19, 0.06). While the mean of the second TFT (T3, T4, TSH) was for group A: (6.33, 246.38, 0.03), group B: (9.18, 318.55, 0.05) and group C: (9.96, 381.72, 0.04). The mean of thyroid uptake for group A, B and C was (21.35, 18.82 and 23.31) respectively. By comparing thyroid uptake average from all the groups, the result showed that thyroid uptake was not affected by the delay period. While the second TFT results showed that there is a direct linear association between T3 and T4 level and the delay period; as the delay period increase T3 and T4 level increase, and TSH level decrease as the delay period increases.  Discussion In conclusion, we demonstrated that Carbimazole 3-days delay period does not interfere with reabsorbing of Technetium-99m in thyroid gland and peripheral tissues. A possible limitation of this study is the number of patients in the sample. Therefore, it seems that it may be possible to perform thyroid scan with a delay period of 3 days rather than 5 or 7 days, this can be time saving and decrease the adverse effects of discontinuing Carbimazole.

Keywords : Hyperthyroidism, Carbimazole, Thyroid Scan, TFT.