Pattern of urine iodine excretion with low iodine diet during preparation for radioactive iodine ablation in patients with thyroid cancer

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 mu g/gCr, respectively, with adequate preparation rate of 93.3% on both days (cutoff value 100 mu g/gCr). In the rhTSH group, the median I/Cr on the 7th and 14th day were 48.0 and 45.7 mu g/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.