[Effects of various contraceptives on laboratory parameters in diagnosis of thyroid gland function with special reference to the free hormones FT4 and FT3].

The effect of different oral contraceptives with an estrogen content of 30-50 micrograms ethinyloestradiol on thyroid hormones and the binding protein TBG was investigated and quantified for 200 women. The sera of 220 normal persons were analysed to get normal values for T3, T4, FT4, Ft3, TBG and TSH. Under the influence of antiovulatory hormone treatment the thyroxin binding globulin increased to values above 32 mg/l in 65% of all euthyroid women. The median for T4 changed from 97 to 120 nmol/l, respectively from 2.3 to 2.8 nmol/l for T3. We think the combination of TSH, FT4 and T3 to be the best analytical tool for differential diagnosis of hyperthyreose. The FT4 level was nearly independent of variations in TBG concentration, so we can accept the normal range from 10-28 pmol/l for patients with contraceptives as well. In 16% of these euthyroid women the T3 level proved to be in the hyperthyroid range with values above 3.6 nmol/l. The FT3 determination is stronger influenced by protein changes caused by oestrogens than FT4 and should not be accepted as a favourite parameter for patients with oral contraceptives.