[Determining serum TBG level using the charcoal-cellulose I-125 thyroxine uptake test]

Radiocompetition method for the determination of blood serum TBG level has been presented. The method is based on binding of 125I-thyroxine by the mixture of cellulose and activated charcoal following the saturation of TBG with L-thyroxine at the concentration of 2.9 nmol/l. The method is similar to the previously described labeled thyroxine uptake in many respects including the use of the same reagents and equipment. The method is simple, easily accessible for any radiochemical laboratory, and yields satisfactory results. The values of TBG obtained with the described method cas serve, together with the values of total thyroxine concentration, for the calculation of free thyroxine index (as TT4/TBG). The above index differentiates well various functional states of the thyroid and serves as a good measure of free thyroid hormones in euthyreosis accompanied by variable TBG values.