Free thyroxine and free thyroxine index in women taking oral contraceptives

This study compares the accuracy of the free thyroxine index and free serum thyroxine radioassay in evaluating the metabolic status of 36 euthyroid women, 17 of whom were taking oral contraceptive drugs. Results indicate that the free thyroxine index does not uniformly compensate for estrogen-induced elevations in total serum thyroxine concentrations and that the free serum thyroxine is the test of choice in assessing the functional thyroid status of women taking oral contraceptive drugs.