[Method for the determination of protein binding of thyroid gland hormones and the detection of antibodies to T4 and T3]

Abstract

More than 99% of circulating thyroid hormones are bound with defined capacity and affinity to transport proteins such as thyroxine binding globulin, albumin and prealbumin. Variants of albumin and/or prealbumin, often familial, will bind T4 and sometimes T3 with increased affinity causing higher TT4 and TT3 values respectively. In determining fT4 and fT3 by analogue tracer its binding to protein variants will also lead to falsely raised free parameters. Thus the possibility of a false diagnosis of hyperthyroidism arises. Also the presence of T4 and T3 autoantibodies will cause misleading findings of increased thyroid hormone parameters as against euthyroid metabolism. For determining the pattern of T4 and T3 protein binding as well as autoantibodies radioactive labelled T4 or T3 is incubated with the patients serum. Transport proteins are separated by means of horizontal agarose gel electrophoresis with water cooling. The gel is sectioned and the activity of individual gel particles is measured in a Gammacounter. The activity graph shows with high precision the binding pattern of T4 and T3 to transport proteins. Moreover, this method also serves to determine any possible T4 and T3 autoantibodies, indicated by a peak in the activity graph in the gamma globulin range.