Laboratory tests
The laboratory reference ranges of thyroid hormones were: TSH: 0.27-4.20 mU/L, T4: 66.00-181.00 nmol/L, free T4: 12.00-22.00 pmol/L, T3: 1.30-3.10 nmol/L, FT3: 3.10-6.80 pmol/L. Standardized criteria of thyroid function were based on the laboratory reference ranges, as follows: normal thyroid function: 0.27≤TSH≤4.2 mU/L and 12.00≤free T4≤22.00 pmol/L. Serum samples were collected between 6:00 and 8:00 AM following an overnight fasting. The tests were completed on the same day at the hospital laboratory. Chemiluminescence procedures (Cobas E610 or 411, Roche, Basel, Switzerland) were employed to determine the thyroid hormones by using Elecsys (TSH, T4, free T4, T3, FT3) kits (Roche Diagnostics Shanghai Ltd, China).