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

[摘要] Many previous studies including ours have reported that athyreotic patients on levothyroxine (LT 4 ) have relatively low serum free triiodothyronine (FT 3 ) levels, whereas patients with large goitrous diseases often have high serum FT 3 levels. Here we investigated Hashimoto thyroiditis (HT) patients on LT 4 to study the relationship between thyroid volume (TV) and thyroid hormone status in hypothyroid patients on LT 4 . We retrospectively studied 408 euthyroid HT patients treated with LT 4 for hypothyroidism; divided them as per TV and compared serum levels of free thyroxine (FT 4 ) and FT 3 and the FT 3 /FT 4 ratio in each patient group with those in euthyroid matched control group. We also evaluated the association between serum FT 3 level and FT 3 /FT 4 ratio and TV among HT patients on LT 4 . In patients with TV <15 mL, serum FT 3 levels were significantly lower than those in controls. In patients with TV 15–80 mL, serum FT 3 levels were equivalent to those in controls. In patients with TV ≥80 mL, the serum FT 3 levels were significantly higher than those in controls. The serum FT 3 level ( r = 0.35, p < 0.01) and FT 3 /FT 4 ratio ( r = 0.42, p < 0.01) showed a positive correlation with TV. TVs in HT patients on LT 4 caused differences in serum thyroid hormone balance, as increasing volume increases the serum FT 3 level and FT 3 /FT 4 ratio. Serum thyroid hormone balance in HT patients with smaller thyroids was similar to that in athyreotic patients. Mild thyrotropin suppression with LT 4 is needed to achieve normal FT 3 levels in such patients.

[学科分类] 内分泌与代谢学

[关键词] Thyrotropin;Triiodothyronine;Levothyroxine;Hashimoto thyroiditis;Hypothyroidism