Serum Sex Hormone—Binding Globulin in Amiodarone-Treated Patients: A Marker for Tissue Thyrotoxicosis

• The iodinated antiarrhythmic drug amiodarone frequently causes an elevation of the serum thyroxine (T 4 ) level in patients who remain clinically euthyroid. Less frequently, true iodine-induced hyperthyroidism may occur. The clinical and laboratory distinction between these two conditions is often difficult. Since the serum sex hormone—binding globulin (SHBG) concentration is elevated in hyperthyroidism, this study was carried out to evaluate the serum SHBG concentration as a possible marker of hyperthyroidism in patients receiving amiodarone. Patients treated with amiodarone were divided into three groups: clinically euthyroid with normal serum T 4 and triiodothyronine (T 3 ) concentrations, clinically euthyroid with elevated serum T 4 and normal T 3 concentrations, and clinically hyperthyroid with elevated serum T 4 and T 3 concentrations. The mean serum SHBG concentration was significantly elevated in amiodarone-induced hyperthyroid patients, while it was normal in euthyroid patients treated with amiodarone who had normal or elevated serum T 4 concentrations. The results suggest that the hyperthyroxinemia induced by amiodarone is not associated with excess thyroid hormone action in the liver unless the serum T 3 concentration is also elevated. ( Arch Intern Med 1987;147:1781-1785)