Tg access

Anti-TgAb was measured by using a competitive radioimmunoassay (Biocode Hycel, Liege, Belgium) with the analytical sensitivity of 6 IU/mL. Anti-TgAb <115 IU/mL was considered as not interfering with serum Tg testing. Serum Tg was measured by using the highly sensitive Tg Access assay (Beckman Coulter, Brea, CA) when patients underwent levothyroxine (L-T4) treatment to avoid interference from elevated TSH. However, patients may hold L-T4 treatment or injection of recombinant human thyrotropin to monitor the disease status of patients during RAI therapy. The blood samples for CEC testing, serum Tg, and other thyroid-related assays were collected simultaneously from one blood drawing.

Serum TSH was assessed by an ultrasensitive enhanced chemiluminescence immunoassay (ECLIA) assay. Serum hormones were measured by microparticle enzyme immunoassay (Abbot AxSYM‐MEIA) with interassay coefficients of variation of less than 10% over the analytical ranges of 1.7–46.0 pmol/L for FT3, 5.15–77.0 pmol/L for FT4 and 0.03–10.0 mU/L for TSH. The within‐run and between‐run precisions for the FT3, FT4 and TSH assays showed coefficients of variation <5%. Measurement of antithyroglobulin antibodies (TgAbs) by an automated chemiluminescence assay system (AntiTg, Ready Pack). Thyroglobulin levels were measured with a second‐generation chemiluminescent Tg immunoassay (Tg Access; Beckman Coulter) with a functional sensitivity of 0.1 ng/ml.