| Abstract: | There is no endocrine contraindication to the use of oral contraceptives (OCs) in a 31-year-old nulliparous woman who presumably is in remission from hyperthyroidism. Yet, several important physiological and pathophysiological alterations must be appreciated to evaluate properly thyroid function in persons taking estrogen-containing preparations. Estrogens induce increased hepatic synthesis and release of thyroxine binding globulins (TBGs). Increased serum TBG concentrations result in a new thyroid hormone equilibrium characterized by an elevated serum thyroxine (T4) level and a reduced resin triiodothyronine (T3 uptake) level but a persistently normal serum-free T4 (FT4) level if the patient is euthyroid. When a patient with an increased serum TBG concentration becomes thyrotoxic, the T4 level rises further and the resin T3 uptake increases from low into the normal range. The calculated FT4 level increases into the thyrotoxic range. Thus, in patients with increased serum TBG levels, the calculated FT4 level is the critical serum determinant for laboratory assessment of thyroid function. If the FT4 level is equivocal in evaluating thyrotoxicosis in the presence of increased serum TBG values, then other clinical and laboratory parameters should be used. A thyroid suppression test or a thyrotropin-releasing hormone test might be useful when the serum parameters are not definitive. It is unnecessary to stop the use of OC preparations to evaluate thyroid function. At this time it is unclear whether the use of estrogen-containing medications influences the nature and extent of an autoimmune remission in Graves' disease. There is some evidence that autoimmune thyrotoxicosis is ameliorated or modified by factors in pregnancy. |
