Determination of Thyroxine Utilizing the Property of Protein-Binding

A simple, rapid method for the determination of serum thyroxine has been described, which is based on the specific binding properties of thyroxine-binding globulin (TBG). One-half ml of the test sample is deproteinized and the thyroxine thus freed is measured according to its competition with a fixed amount of thyroxine-I131 for a fixed amount of TBG. The method is highly specific for thyroxine, and is unaffected by iodine or mercury contamination. The mean value expressed as thyroxine iodine for euthyroid individuals was 6.6±1.3 μg/100 ml, with a range of 4.0–9.2, corresponding to a mean thyroxine level of 10.1 μg/100 ml (range 6.1–13.8). A good correlation was obtained with the clinical status of patients studied.