A Method for the Determination of Free, Non-Protein Bound Thyroxine in Serum

Abstract

It is highly probable that it is the free, nonprotein-bound thyroxine that is decisive for the peripheral utilization of the hormone. In the present paper a method for determination of this free thyroxine is presented. The method involves a determination of the proportion of a given quantity of added radioactive thyroxine that remains unbound. The magnitude determined by this procedure may be considered approximately inversely proportional to the level of unsaturated protein receptors for thyroxine.