Pertechnetate uptake in the prediction of early outcome after radioiodine therapy

99mTc-pertechnetate uptake was estimated 8-13 weeks after radioiodine therapy for hyperthyroidism in 132 patients in order to evaluate the usefulness of the uptake test in predicting both persisting hyperthyroidism and the early onset of hypothyroidism during the first year after therapy. The estimation was simple, the result immediately available, and its sensitivities, positive predictive value and its overall accuracy (83%) compared favourably with that of in-vitro tests, FT4I (75%) and FT3I (80%), carried out on the same occasions during the early follow-up period. Pertechnetate uptake can be a useful guide to management by promptly identifying patients likely to need further radioiodine therapy and those with transient or permanent hypothyroidism. The study confirmed some previous findings that hypothyroidism was more frequent in patients with thyroid antibodies and less frequent in patients with nodular thyroids, and it also indicated that hypothyroidism was more frequent in those treated with carbimazole before and after radioiodine, and that hyperthyroidism was more likely to persist in those treated with carbimazole before or after radioiodine.