Reliability of early iodine 123 uptake for treatment of Graves disease in children.

Objective: To determine the reliability of early radioiodine uptake (RAIU) in calculation of the radioiodine ablation dose for pediatric patients with Graves disease.

Methods: This retrospective review of medical records involved 22 pediatric patients with Graves disease, who had undergone early (4 to 8 hours) and late (24 to 26 hours) RAIU studies and were treated with iodine 131 (131I). Quantitative data are reported as mean ± standard error of the mean. Early and late RAIU and actual administered versus calculated 131I ablation doses were compared by using the paired t test. The correlation between early and late RAIU was assessed by curvilinear regression analysis. Significance was assessed at P<.05.

Results: Mean early RAIU was 57.1% ± 18.2%, and mean late RAIU was 72.1% ± 14.4% (P<.05). Curvilinear regression analysis showed the following: late RAIU = 7.13 + 1.71 × (early RAIU) - 0.01 x (early RAIU)2; r2 = 0.75. The mean ablation dose of 131I based on late RAIU was 9.3 ± 2.0 mCi. The calculated radioiodine dose would have been, on average, 32% higher (12.3 ± 3.8 mCi; P<.05) had early RAIU been used.

Conclusion: In children, early RAIU can be much lower than late RAIU. This may be misleading for ablation dose calculations. Therefore, late RAIU should be used to avoid overtreatment in children with Graves disease.