2.3. Biochemical Measurements of Thyroid Function and Antibodies

Serum levels of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4), total triiodothyronine (TT3), and total thyroxine (TT4) were determined by using chemiluminescent immunoassays (Abbott Diagnostics, Tokyo, Japan). The reference ranges were 0.27–4.2 uIU/mL for TSH, 2.02–4.43 pg/mL for FT3, and 0.93–1.71 ng/dL for FT4. The measurements of serum thyroid autoantibodies (TPOAb or TGAb) were performed by using chemiluminescent immunoassays (Beckman Coulter, Fullerton, CA, USA). The reference ranges for TGAb and TPOAb were defined as less than 115 U/mL and smaller than 34 U/mL, respectively.