Lack of association between urinary iodine excretion and successful thyroid ablation in thyroid cancer patients

Background: Low-iodine diet is prescribed before 131I administration in patients with differentiated thyroid cancer, although no study has properly quantified its clinical benefit. Objective: Our study aimed to evaluate the association between urinary iodine excretion (UIE) and 131I ablation by correlating UIE with the rate of successful ablation. Patients: We retrospectively studied 201 differentiated thyroid cancer patients who had received 131I therapy and posttherapy whole-body scan (WBS) for remnant ablation after either thyroid hormone withdrawal (THW group, n = 125) or recombinant human TSH (rhTSH group, n = 76). The outcome of thyroid ablation was assessed using two different criteria: no visible uptake at control WBS 8-12 months after ablation or no visible uptake plus undetectable stimulated serum thyroglobulin (Tg). Results: According to the criterion of no visible uptake, 84.6% of the patients were successfully ablated, with no significant difference between THW and rhTSH groups. Mean UIE at the time of ablation was 132 ± 160 μg/liter, not significantly different between patients of theTHW and rhTSH groups. There was no significant difference in UIE between ablated or nonablated patients both in the whole group and the rhTSH or THW groups. According to the criterion of no visible uptake plus undetectable stimulated serum Tg (in anti-Tg negative patients) at control WBS 8-12 months after ablation, UIE was not significantly different in ablated and nonablated patients. Conclusions: Our study indicates that the body iodine content is not an important determinant of thyroid ablation, when preparing the patients with either THW or rhTSH. Copyright © 2010 by The Endocrine Society.