Radioiodine therapy in hyperthyroid disease: poorer outcome in patients with high 24 hours radioiodine uptake

Summary Purpose:  To evaluate the importance of 24 h radioiodine uptake (24 h RIU) for the outcome of radioiodine treatment of hyperthyroidism. Methods:  Retrospective analysis of 72 patients who underwent radioiodine treatment for toxic goiter at our outpatient clinic [29 diffuse goiters (DG), 30 toxic multinodular goiters (TMG) and 13 toxic adenomas (TA)]. Thyroid status was determined by TSH, fT3 and fT4 levels, and outcome was rendered successful when hyperthyroidism was absent. Relation between low 24 h RIU (below median) or high 24 h RIU (above or equal to median) and outcome was evaluated. Results:  Of patients with DG and low 24 h RIU, 15% remained hyperthyroid, as opposed to 56% of patients with DG and high 24 h RIU ( P <0·05). Of patients with TMG and low 24 h RIU, none remained hyperthyroid, as opposed to 44% of patients with TMG and high 24 h RIU ( P <0·01). Of patients with TA and low 24 h RIU, none remained hyperthyroid, as opposed to 43% of patients with TA and high 24 h RIU (NS, P  = 0·19). Conclusion:  In patients with hyperthyroid disease treated with radioiodine the outcome is poorer for patients with high 24 h RIU compared with low 24 h RIU measured prior to treatment when the radioiodine dose is calculated on the basis of 24 h RIU.