TSH and thyroid hormones concentrations in patients with hypothyroidism receiving replacement therapy with...

The aim of this study was to evaluate parameters of thyroid function in patients with primary hypothyroidism receiving either monotherapy with L-T4 or combination L-T4+L-T3. Fifty-eight women with primary hypothyroidism receiving L-T4 were enrolled in the study. The patients were randomised into two groups: Group 1 (n=42) patients continued monotherapy with L-T4, and Group 2 (n=16) patients were switched to combined therapy with L-T4+L-T3 (25 microg L-T4 was replaced with 12.5 microg L-T3). The final examination was carried out 6 months thereafter. There was also a third group of 20 healthy women (control group). Under monotherapy with L-T4, serum FT4 levels were higher (p < 0.05) and FT3 lower (p < 0.05) than in the control group, while the monotherapy subgroup of patients with low-normal TSH had serum FT4 levels higher than in the control group (p < 0.05). Serum FT4 under combined therapy was significantly lower than in both control and monotherapy groups. FT3 levels did not differ between the two groups of combined and monotherapy subjects; the highest FT3 levels were in the control group. L-T4 replacement therapy is associated with non-physiologically high FT4 and low FT3 levels. Therapy with L-T3 once a day does not simulate the normal production of T3 by the thyroid.