[Effects of amiodarone on thyroid hormonal profile. Updating based on new assay methods]

Amiodarone (A) treatment alters the levels of thyroid hormones. We investigated whether new hormonal assays are also altered by this drug. Thyroid function was determined in 21 patients chronically treated with A and in 30 controls. TSH was determined with a third generation assay. Free T3 and Free T4 levels were determined by 5 different immunoassays. Equilibrium dialysis (E.D.) was considered as the reference assay for FT3 and FT4. With this method FT3 is diminished, reverse T3 ans FT4 are increased whereas TSH remained normal. Only FT3 determined by an assay using a labelled monoclonal antibody (MAB) appears not modified by A. Other methods (chromatography, chemiluminescence and radioisotopic) give results in agreement with E.D. Some of these alterations may be explained by a marked increase in plasma levels of non esterified fatty acids. Hormonal changes induced by A are typically with all but one assays. Whatever the method used the determination of TSH remains necessary to avoid misinterpretation of the thyroid function tests in A-treated patients.