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

Abstract

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.

PIP: The effect of various contraceptives on thyroxin binding globulin (TBG) and the thyroid hormones T4 (thyroxin) and T3 (triiodothyronine) was investigated, and also whether the determination of the free hormones FT4 and FT3 meets expectations. The normal values of T3, T4, FT4, FT3, TBG, and TSH (thyroid-stimulating hormone) were ascertained in 220 people aged 18-70 years, (45% men and 55% women) by radiometric means. Thyroid function was studied in another group of 200 women aged 18-50 years who were taking various oral contraceptives (OCs) for at least 6 months. 107 euthyroid women not taking OCs served as controls. OCs used included Minisiston, Trisiston, Gravistat, Nonovlon, Sequostat, Ovosiston, and Deposiston. Patients were divided in euthyroid and hyperthyroid groups. T3, T4, and TSH determination was also verified in a group of 80 normal people. 65% of OC using euthyroid women had increased TBG levels, mostly under 50 mg/l. 23% of OC using euthyroid women had a T4 level of over 140 nmol/l and 27% had a T3 level above 3.3 nmol/1. Only 40% of women had both an elevated T4 and T3 level. TBG and total T4 and total T3 had weak correlation: coefficients of .33 and .21, respectively. In euthyroid OC users the median T4 values of 97 nmol/l shifted to 120 nmol/l, with the highest range of 140 nmol/l and 170 nmol/l. In euthyroid nonuser women the median T3 value was 2.3 nmol/l, increasing to 2.8 nmol/l in OC users. The average value of the TBG level with all OCs was in the range of 34-40 mg/l: it was over 50 mg/l in 13 cases, mostly with 50 mcg of ethinyl estradiol (EE). 21 hyperthyroid OC users had T3 values of 4 nmol/l and average TBG levels of 30.0 mg.l. In the diagnosis of hyperthyroidism in 90% of OC users the combination of basal TSH, FT4, and T3 can lead to clarification, provided a grey area of 4 nmol/l is accepted for T3. In the rest, TBG and FT3 determinations are also necessary.