Thyroid uptake of radioactive iodine in hyperthyroidism

We compared the 24-hour uptake of radioactive iodine (RAIU) in hyperthyroid patients diagnosed from 1970 to 1972 (Group A) and from 1975 to 1976 (Group B). Mean RAIU values in Group B decreased from those in Group A. In 1969 we lowered the normal range for the RAIU test to 0% to 24%, and used the new range for the diagnosis of hyperthyroidism in both groups of patients. The RAIU in Group B is within normal limits in 14% of the patients with Graves' disease and 80% of the patients with toxic nodular goiter (TNG). This study demonstrates that in our geographic area, the 24-hour RAIU has become a poor test for the diagnosis of hyperthyroidism, particularly TNG. However, the test should be performed before radioactive iodine therapy because it is necessary in calculating the therapeutic dose.