Association between serum thyroid hormone balance and thyroid volume in patients treated with levothyroxine monotherapy for hypothyroidism

[Abstract.] Many previous studies including ours have reported that athyreotic patients on levothyroxine (LT4) have relatively low scrum free triiodothyronine (FT3) levels, whereas patients with large goitrous diseases often have high scrum FT3 levels. Here we investigated Hashimoto thyroiditis (HT) patients on LT4 to study the relationship between thyroid volume (TV) and thyroid hormone status in hypothyroid patients on LT4. We retrospectively studied 408 euthyroid HT patients treated with LT4 for hypothyroidism; divided them as per TV and compared serum levels of free thyroxine (FT4) and FT3 and the FT3/FT4 ratio in each patient group with those in euthyroid matched control group. We also evaluated the association between serum FT3 level and FT3/FT4 ratio and TV among HT patients on LT4. In patients with TV -80 mL, the serum FT3 levels were significantly higher than those in controls. The serum FT3 level (r=0.35, p