I131 has been used with increasing frequency since its introduction over 20 years ago as therapy for thyrotoxicosis. With most therapeutic regimens 30%-40% of patients require mutiple doses of I131 to obtain complete clinical remission.1-3 An important practical consideration is to select as soon as possible after initial therapy the patients who will need re-treatment so that the symptoms can be brought under control with a minimal lapse of time.
Of the many methods available for estimating thyroid function, measurement of the accumulation of radioactive iodine (RAI) affords the most direct and immediate indication of the state of thyroid cellular function. The PBI, cholesterol, and basal metabolism reflect primarily the pool of residual thyroid hormone. The usefulness of the 24-hour I131 uptake at intervals after I131 therapy has been previously reported by others. Schultz and Zieve,4 Domnitz et al,5 Larsson and Ragnhult,6 and Myant 7 indicated varying degrees of usefulness
GELLER J, RETTIG J. Prognostic Value of 24-Hour Radioactive Iodine UptakeStudies in Patients With Nodular Goiter and Diffuse Hyperplastic Goiter Eight to Ten Weeks Following Therapy With Radioiodine (I131). Arch Intern Med. 1964;114(2):247–250. doi:10.1001/archinte.1964.03860080097009