The Urinary Iodine Level Based on Different Duration of Low-Iodine Diet for Radioactive Iodine Therapy.

Background/Objective: The optimal period of a low-iodine diet (LID) during preparation for radioactive iodine therapy (RAI) is not well established. At the University of Washington, we conducted a retrospective analysis of patients with a diagnosis of differentiated thyroid cancers who underwent total thyroidectomy and RAI during the period 2022-2024 and compared urine iodine concentration in patients who had either 1 or 2 week of LID prior to RAI. Case Report: All analyses were performed using SAS software 9.4 (SAS Institute). There were 72 patients who met the criteria. The median age of this cohort was 46 years (range: 19-82) and 63.9% were female. Of these, 53 patients underwent a 1-week and 19 patients underwent a 2-week LID before RAI. The median value of urine iodine after a 2-week restriction was lower at 0.228 μmol/L (29 μg/L) (range: <0.079-1.481 μmol/L; <10-188 μg/L) compared to 1 week at 0.362 μmol/L (46 μg/L) (range: <0.079-30.43 μmol/L; <10-3863 μg/L), but not statistically significant ( Discussion: Although the urine iodine level was lower in 2-week restriction, there was no statistically significant difference between 1 versus 2-week iodine restrictions following RAI. This suggests that a 1-week LID may be adequate for RAI treatment. This would decrease time to treatment for patients and decrease the burden of LID. Conclusion: There is a need for future large prospective randomized control trials to identify the optimal duration of LID and determine the goal urinary iodine level for successful RAI ablation.