THE BEHAVIOR OF RADIOIODINE IN THE BLOOD 1

Open Access
Publisher Website
Google Scholar
Abstract
Levels of total radioiodine in the blood after oral ingestion of I131 in the form of iodide show significant differences in various thyroid states. 8 hrs. after ingestion, the mean concn. of radioiodine in the serum was 2.06% of the dose per liter in cases of myxedema, 1.28% in euthyroid persons and 0.49% in cases of hyperthyroidism. The curve of total radioiodine in serum plotted against time has 3 components: (a) an initial rapid increase followed by a brief, rapid fall, regarded as reflecting gastro-intestinal absorption and equilibration with body fluids; (b) an exponential fall, regarded as reflecting disappearance of radioiodine as iodide from the blood into the thyroid, the urine and other sites of disposal, and (c) a 3d phase which indicates the appearance in the blood of organically bound radioiodine. The rate of disappearance of radioiodine from the blood reflects variations in thyroidal function, being more rapid than normal in hyperthy-roid subjects and less rapid than normal in hypothyroid ones. Comparison of the rate of disappearance of radioiodine from blood estimated directly from blood itself with estimations of the same rate detd. from simultaneous observations of urinary excretion of radioiodine did not disclose any significant difference. The latter method therefore appears to be an appropriate means of estimating the disappearance rate of radioiodine from blood. Precipitable radioiodine appeared in the blood much sooner, rose more rapidly and reached higher concns. in hyperthyroid than in euthyroid persons. A small concn. of precipitable radioiodine was observed in a patient who had myxedema.
Keywords