Clinical Usefulness of the I131 Triiodothyronine Erythrocyte Uptake Test

Abstract

In a series of 1,033 patients seen over a period of 25 months, 1,223 determinations of the in vitro I¹³¹ triiodothyronine uptake of red blood cells (T3 RBC uptake rate) were completed. The results of routine protein-bound iodine and radioiodine thyroid uptake tests and the final clinical impression were correlated with the results of this test. Of the euthyroid patients 667 (85%) had normal T3 RBC uptake values, while 115 (14.7%) had unexplained elevations of the rate of T3 RBC uptake; of 121 hyperthyroid patients, 98% had supportive results to the T3 RBC uptake studies, and, of 33 hypothyroid patients, 27 had correlative results. The various disease states and technical artifacts that influence this test are mentioned. The T3 RBC uptake determination is established as a supportive test in the evaluation of thyroid status.