Should the assay of serum free thyroxine and triiodothyronine replace the other methods of evaluating thyroid function?

Total T4, total T3, free T4 and free T3 were measured at the same time in 633 subjects. These subjects were classified according to the clinic state and the hormonal results in 426 euthyroid, 145 hyperthyroid and 62 hypothyroid cases. The results permitted to define the sensitivity, specificity and predictive value of the different tests. When each measure was considered alone, free T4 was the most useful test for all the hormonal states. In association, FT4 + FT3 is more useful than T3T + T4T for all the diagnostic parameters and for all the clinical situations. To measure FT4 with an adequate kit appears to be in 1985 the key method for evaluating the thyroïd function. To associate FT3 is useful in some difficult cases.