Background: The optimal period of low iodine diet during preparation for radioactive iodine (RAI) ablation in an area with iodine-rich diet was investigated. Methods: Ninety-four patients with thyroid cancer who underwent low iodine diet and RAI were prospectively allocated into 2 groups—thyroxine withdrawal or using recombinant human thyroid stimulating hormone (rhTSH) for TSH stimulation. Their urinary iodine excretion (UIE) patterns were analyzed. Results: There was no clinicopathological difference between the 2 groups except for tumor size and lymph node status. The UIE (median iodine to creatinine ratio, I/Cr) in the withdrawal group on the 7th and 14th day were 18.3 and 17.9 μg/gCr, respectively, with adequate preparation rate of 93.3% on both days (cutoff value 100 μg/gCr). In the rhTSH group, the median I/Cr on the 7th and 14th day were 48.0 and 45.7 μg/gCr (adequate preparation rates 91.8% and 93.8%), respectively. Conclusion: One week of low iodine diet is sufficient preparation for RAI regardless of method of TSH stimulation.
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