The predictive role of 24h RAIU with respect to the outcome of low fixed dose radioiodine therapy in patients with diffuse toxic goiter

Radioactive iodine uptake (RAIU) is a test used to differentiate hyperthyroidism from thyroiditis and to calculate the radioiodine dose for treatment of Graves' disease. We aimed to evaluate the predictive role of 24h RAIU with respect to the outcome of radioiodine therapy in patients with diffuse toxic goiter (DTG). Methods: Case records of patients with DTG treated with radioactive iodine were reviewed retrospectively. Patients were divided into two groups based on 24h RAIU (normal range: 15% - 35% at 24 h): the first group included patients with 24h RAIU values equal to or less than 50%, while the second group included patients with 24h RAIU values of over 50%. Gland size, duration of disease, treatment with antithyroid drugs (ATD) and its duration were the other factors considered. Success of the first dose of I-131 was defined as a euthyroid or hypothyroid status at 12 months post-therapy without the need for additional radioiodine or ATD therapy. Data were analyzed with 95% power and 1% type I error (alpha=0.01). Results: Six hundred thirty-three (633) consecutive patients with DTG were given a fixed-dose (5mCi) of radioiodine between January 1987 and December 2006. One hundred seventy-five patients (175) had an RAIU <= 50% and 458 patients had an RAIU >50%. First-dose success rate in the former group was 81.7% and in the second group 68.6% (p=0.001). The overall first-dose success was 72%. Multivariate analysis confirmed the significant role of 24h RAIU data to predict a successful outcome. Conclusion: A 24h RAIU value of <= 50% appears to be associated with a significantly better outcome compared to that of a 24h RAIU value of >50% in patients with DTG given as treatment a fixed dose of 185 MBq radioiodine.