[Evaluation of the optimal thyroxine dose with the TRH test for replacement and suppression therapy]

53 patients with overt hypothyroidism (group 1), 17 patients with "preclinical hypothyroidism" (group 2), 22 patients with a euthyroid goiter (group 3) and 13 patients who had undergone total elimination of the thyroid gland for thyroid cancer (group 4) were treated with thyroxine. Basal levels of T4, T3, TSH and the TSH-response to 40 mg oral TRH were measured during treatment. For replacement therapy in hypothyroid patients of group 1 and 2 the dose was adjusted until the TSH response to TRH was within the normal range (3.5-38 mU/l). In groups 3 and 4 the thyroxine dose was increased to suppress the TSH response to TRH in the presence of euthyroid T4 and T3 levels (suppressive dose). Average thyroxine replacement doses were 128 micrograms per day in overt hypothyroidism and 101 micrograms/day in preclinical hypothyroidism. Suppressive doses of thyroxine were on average 119 micrograms/day in patients with euthyroid goiter and 183 micrograms thyroxine per day in patients with total thyroid ablation. In all 4 groups of patients a wide interindividual variation of the optimal thyroxine dose was found.