Oral contraceptives and thyroid function tests

Contraception in autoimmune diseases

Autoimmune diseases (AIDs) affect women and men with a 2:1 ratio, which suggests that hormonal contraceptives play a role in their clinical course. Combined oral contraceptives have complex, sometimes contradictory, effects on AIDs; they can worsen the situation in women with systemic lupus erythematosus and with anti-phospholipid syndrome, conditions in which they are contraindicated. Early studies indicated a positive effect on rheumatoid arthritis (RA), whereas more recent trials failed to do so, possibly because of the lowering of oestrogen content. Evidence of effects on multiple sclerosis (MS) is conflicting: risk may vary depending on the progestin used. Minor adverse effects may exist on inflammatory bowel diseases, and no significant effect was found on autoimmune thyroid diseases. Women can become sensitised to sex hormones. Progestin-only contraceptives may be used, although copper-releasing intra-uterine devices represent the best option. Finally, several organisations have issued guidelines for contraceptive use in women with AIDs.

Pharmacological interference with in vitro tests of thyroid function

Numerous drugs may cause changes in the serum concentrations of T4 and of T3. If such alterations are not recognized an incorrect diagnosis may result. In moderate degrees of hypo- and hyperthyroidism thyroid hormone levels may be spuriously normal, or the influence of pharmacological substances may lead to false diagnosis of thyroid disease in euthyroid patients. Since prediction of such alterations remains uncertain, it may be necessary to perform additional investigations when a potential artefact is recognized. On the other hand many pharmacological agents, especially those which interact with neurotransmitters, may influence TSH secretion, too. The TRH-test may show an increase or decreased TSH response, although complete suppression is only rarely seen during high-dose glucocorticoid treatment when low TRH doses are applied. Because of TRH-test gives such wide separation between different clinical states false interpretations are generally less likely than with drug-induced changes in T4 and T3 values.

The effect of age, sex and other factors on blood chemistry in health

Quantitative data is presented concerning the influence that age, sex, the menopause, oral contraception, blood group and time of blood collection have on 19 commonly-determined blood chemistry values. The data were derived from 1000 healthy blood donors in whom blood sampling conditions were standardised to conform with those applying to hospital out-patients. Statistical techniques were used to allow for the effects of analytical variation and to enable the effects of the various factors and their interactions to be expressed in a practically useful manner. Age and sex effects are shown to be the rule and to interact in many instances. Creatinine, urea, glucose, cholesterol, potassium and globulin show a tendency to increase in concentration with age, while total protein, albumin, calcium, inorganic phosphate and iron levels tend to fall progressively. Evidence is given to suggest that many of the changes occurring in women at about 50 years should be attributed to hormonal changes. In all instances when the menopause has a significant influence there is a rise in the concentration of the constituent concerned. It is proposed that other laboratories should assemble age and sex stratified reference ranges from (a) figures given for the mean values for defined age and sex groups, adjusted if necessary to allow for different analytical bias, (b) figures given for nonsystematic biological variation, and (c) their own measurements of analytical precision. Details of the necessary procedure are given, allowance being made for logarithmic transformation of the results where necessary.

Assessment of thyroid function during pregnancy

Serum levels of thyroid stimulating hormone and of the two thyroid hormones were compared in pregnant women and in non-pregnant control subjects. Circulating levels of thyroid stimulating hormone did not alter significantly throughout pregnancy. Total thyroxine and triiodothyronine concentrations increased markedly during the first and second trimesters, associated with a progressive increase in the thyroid binding capacity of serum proteins. Urinary triiodothyronine and thyroxine excretion during the third trimester of pregnancy was comparable to that found in non-pregnant euthyroid females and, it is concluded, provides the simplest method of assessing thyroid function during pregnancy.

Effects of oestrogen on urinary thyrosine excretion

The day to day variation and the effects of oestrogen on the urinary excretion of thyroxine (T-4) were studied in euthyroid women and men. Serial urinary T-4 values over a period of 28 consecutive days were found to lie within relatively narrow limits except for a transient increase during menstruation in women. During oestrogen therapy urinary T-4 was unchanged, but an appreciable rise was seen after stopping oral ovulation inhibitors in women. A similar effect was seen in men after three days' treatment with 20 mug/day of ethinyloestradiol. The increased urinary T-4 excretion on oestrogen withdrawal reached a maximum in one to three days. This response contrasted with that produced by phenytoin, a drug known to bind to thyroxine binding globulin, and which resulted in increased urinary T-4 excretion during the period that it was being administered.

Failure of a pure progestogen contraceptive to affect serum levels of iron, transferrin, protein-bound iodine, and transaminase

Medroxyprogesterone acetate, a pure progestational agent which is not metabolized to oestrogen, was given to 30 women and shown to have no effect on the serum levels of iron, total iron-binding capacity, transferrin, and protein-bound iodine. Eighteen of these women had previously taken oral contraceptives of the combined oestrogen-progestogen "sequential" type, and during that time these serum levels were raised. Nevertheless, the levels all fell significantly after medroxyprogesterone acetate was given and the "sequential" oral contraceptive was stopped. In a further 12 postpartum women the serum levels did not change significantly after medroxyprogesterone acetate.These observations strongly suggest that raised plasma protein levels resulting from the administration of oral contraceptives are due to the oestrogen component.