Determination of serum thyroxine using a resin sponge technique.

A method is described for the determination of serum thyroxine using ion-exchange resin sponges. The principle is based on the use of protein-binding sites and part of the technique is similar to the Triomet resin uptake test. An isotope extraction recovery procedure is incorporated in the method. Studies of factors influencing the analysis are reported and the results of tests of accuracy, precision, and specificity are presented. Serum thyroxine iodine values are compared with protein-bound iodine estimations. The values found in health and disease are similar to the results of previous workers. The specificity of the analysis represents a considerable advantage over protein-bound iodine determinations since no interference is caused by iodides, iodine-containing contrast media, mercurial diuretics, mono-iodotyrosine, di-iodotyrosine, di-iodothyronine, and also tri-iodothyronine in physiological amounts. Therapy with diphenylhydantoin and tri-iodothyronine will tend to depress protein-bound iodine levels and thyroxine values are similarly influenced.