Association Between Excessive Urinary Iodine Excretion and Failure of Radioactive Iodine Thyroid Ablation in Patients with Papillary Thyroid Cancer

作者：Sohn Seo Young; Choi Joon Young; Jang Hye Won; Kim Hye Jeong; Jin Sang Man; Kim Se Won; Suh Sunghwan; Hur Kyu Yeon; Kim Jae Hyeon; Chung Jae Hoon; Kim Sun Wook

来源：Thyroid, 2013, 23(6): 741-747.

DOI：10.1089/thy.2012.0136

Background: A low-iodine diet (LID) is usually recommended for a week or two before radioactive iodine (RAI) ablation therapy in papillary thyroid cancer (PTC) patients after total thyroidectomy. However, it is still controversial whether an LID affects ablation outcomes. We therefore evaluated the association between urinary iodine excretion and the rate of successful ablation and investigated the determinants of successful RAI ablation outcomes. %26lt;br%26gt;Methods: We retrospectively reviewed the records of 295 consecutive patients with PTC who received 1110MBq RAI remnant ablation therapy with thyroid hormone withdrawal after total thyroidectomy. Successful ablation was defined as either no visible or faint uptake on a follow-up scan (definition 1), or no visible or faint uptake on a follow-up scan and a stimulated thyroglobulin level %26lt;2 ng/mL (definition 2). %26lt;br%26gt;Results: The proportion of patients with appropriate LID status (defined as a urinary iodine concentration [UIC] %26lt;66.2 mu g iodine/g creatinine [mu g/gCr]) was significantly higher in the successfully ablated group (81% vs. 67%, p = 0.03). Based on definition 1, 80.3% (237/295) of patients were successfully ablated. The ablation rate was significantly lower in patients who had a UIC %26gt;250 mu g/gCr at the time of RAI ablation (p%26lt;0.05). In multivariate analysis, a UIC %26gt;250 mu g/gCr was the only significant variable associated with ablation failure (p = 0.002, odds ratio [OR] 4.74 [95% confidence interval (CI) 1.78-12.63]). Based on definition 2, 74.9% (221/295) of patients were successfully ablated. A UIC %26gt;250 mu g/gCr at RAI administration showed a significant association with ablation failure (p%26lt;0.05). The OR of a UIC %26gt;250 mu g/gCr for ablation failure was 3.88 [CI 1.42-10.57] (p = 0.008). %26lt;br%26gt;Conclusion: Excessive iodine intake (UIC %26gt;250 mu g/gCr) was associated with poor RAI ablation outcomes. Because this amount of iodine is very high, we propose that the level of strictness of the LID protocol should be modified according to the region that the patient is from and the food that the patient is accustomed to eating. Even in those areas where iodine intake is high, overly strict compliance with an LID protocol is not necessary and simple recommendations to avoid iodine-rich foods would be appropriate.

• 出版日期2013-6