Evaluation of methods of measuring the accumulation of I 131 by the thyroid gland.

A little over fifteen years has passed since it was shown by Hertz et al. (8) and Hamilton (7) that radioactive iodine could be put to good use in studying thyroid physiology. Most of the earlier thyroid function studies consisted in indirect measurements of the amount of a tracer dose of radioactive iodine excreted in the urine over a twenty-four to seventy-two-hour period (10, 23, 24, 25, 28). These tests were based on the premise that the thyroid gland was the only tissue which utilized iodine to any extent, and that amounts which were not metabolized were rapidly excreted in the urine. Keating and his group (11) extended these studies to show that more diagnostic information could be obtained if serial samples of urine were collected during the early hours of the test and assayed for radioactivity. If these samples were plotted against time, the renal excretion rate could be calculated, and from this the extrarenal (or thyroidal) rate of accumulation could be determined. While fairly accurate results ...