Importance of free thyroxine in comparison with total thyroxine in thyroid exploration

ABSTRACT

The authors report a study about the more discriminative value of FTA versus TT4 in thyroid investigation. 196 patients have been tested - 33 normal subjects. 48 patients suffering of hyper [n =24] or hypothyroidism [n = 24]. 115 patients who are clinically euthyroid but with disturbed TBG [75 impregnated with oestrogen, 17 undergoing a corticotherapy and 23 suffering of nephritic syndrome]. Their TT4, ET4 and TSH have been assedded by radioimmunoassay. In normal and dysthyroid patients the values of their three hormones agree with each other. The clinical euthyroid state of the third group is confirmed by their normal FT4and TSH values. Their apparent TT4 values are influenced by the disturbed value of their TBG [p < 0.0001].The assessment of FT4 associated to TSH seems to be an accurate test to investigate the thyroid function and the binding proteins