THE UPTAKE OF 131I TRIIODOTHYRONINE BY RESIN. AN IN VITRO TEST OF THYROID FUNCTION

ABSTRACT A technique is described, which resembles the in vitro red cell triiodothyronine uptake test for the investigation of thyroid function, but which requires only 0.5 ml of plasma. The uptake of radio-triiodothyronine is measured by a method in which resin replaces the erythrocytes. Thus the variable of the red cell substrate is excluded. By means of the resin technique described, an uptake of 14–27 % was found in a group of 130 euthyroid subjects. Fourteen plasma samples from hyperthyroid patients were investigated, which showed an uptake range of 25–40 % (one plasma sample from this group had an uptake of 25.8, i. e. within the normal range). In one case of hypothyroidism, an uptake of 10.7 % was found. It is not yet possible to state the level of uptake below which the diagnosis of hypothyroidism should be considered. The effect of different factors like the quantity of resin, incubationtemperature and incubation-time, pH and others have been investigated. The results are discussed.