Serum concentrations of 3,5,3',5'-tetraiodothyroacetate (T4A) in subjects with hypo-, hyper- and euthyroidism.

Some factors influencing serum 3,5,3',5'-tetradiodothyroacetate (T4A) concentrations were examined in hypothyroid, euthyroid and hyperthyroid human subjects. Serum T4A concentration was shown to be correlated with parameters such as serum, total and free thyroxine (T4) concentrations and thyroxine: thyroxine binding globulin ratio, which are indicative of the availability of T4 for peripheral metabolism. The relationship between T4A and these parameters was not a simple linear one; serum levels of T4A tended to show less variation from the normal range than did serum total T4 in hyperthyroid subjects.