JOURNAL OP NUCLEAR MEDICINE 5:657-663, 1964 A Fifteen Minute Test of the Rate of Thyroid Trapping of Radio-Iodine

Over the years a number of reports have been published dealing with early uptake measurements of radioactive iodine by the thyroid gland ( 1,2,3,4,5,6,7), particularly within the first 60 minutes. In general, the measurements have been more satisfactory in distinguishing hyperthyroidism from euthyroidism than the conventional 24 hour uptake, but of no practical help in diagnosing hypothyroid ism (3,6). These authors used the per cent of administered dose accumulated in the gland as an index of functional capacity. In the test to be described in this paper continuous counts over the thyroid are obtained on a strip chart recorder after an intravenous injection of radioactive iodine in much the same manner as de scribed by Larsson and Johnsson (4), Higgins (3) and Mosier (6). Instead of counting a separate standard and determining a per cent uptake of radioactivity in the gland after a given interval, a simple ratio of the net counts at 15 minutes to that at 5 minutes is obtained (R1,). This ratio, called the trapping index (R15), the 24 hour uptake (T24) and the clinical state are compared in 310 patients