THE URINARY EXCRETION OF RADIOIODINE IN VARIOUS THYROID STATES

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Abstract
The urinary excretion of radioiodine following its oral admn. was studied in normal subjects, euthyroid patients who had low-grade thyroid malignant lesions, patients who had myxedema, and patients who had untreated exophthalmic goiter. The urinary excretion curves differed significantly among the euthyroid, hypothyroid, and hyper-thyroid groups. Mathematical analysis of the urinary excretion yielded the following 4 quantities: (1) the renal fraction (which is the fraction of the dose of radioiodine primarily excreted in the urine); (2) the disappearance rate (which is the proportional rate of disappearance of radioiodine from the blood); (3) the renal excretion rate (which is the proportional rate of excretion into the urine), and (4) the collection rate (which measures the proportional rate of disappearance into sites other than the kidneys). Insofar as the thyroid represented the chief site in the body for collecting I, the last of these 4 values served as an index of thyroid-collection rate. When the radioiodine curve of the thyroid was determined by observations obtained from the subject''s thyroid directly, the true rate of collection by the thyroid could be estimated. Estimations of disappearance rate, based on analysis of renal excretion, agreed fairly closely with estimations of the same quantity based on direct measurements of blood samples, measurements of the thyroid in vivo and measurements of peripheral radioactivity in vivo. The renal fraction was greater than normal in hypothyroid patients and was less than normal in hyperthyroid patients. The disappearance rate was less in hypothyroid patients than in normal subjects and was markedly greater than normal in cases of hyperthyroidistn. Significant individual variations occurred in renal excretion rates but no significant differences were observed in the mean renal excretion rates among the 4 groups of cases studied. The most significant variation observed occurred in the collection rates, which were very much less than normal in the hypothyroid cases, and averaged 6 times the normal in the hyperthyroid patients. The significance, the limitations, and the possibilities of this technique were discussed.