Laboratory measurements
THYROID
All laboratory measurements were determined on -20ºC stored serum samples. The thyroid function tests including TSH, T3, T4, and free hormones were measured by electrochemiluminescence immunoassay method using Roche Diagnostics kits on the Cobas e- 411 automated analyzer (Roche Diagnostics, GmbH, Mannheim, Germany). The sensitivity of TSH, T3, T4, FT3, and FT4 assays were 0.005 µIU/mL, 0.195 ng/mL, 0.420 µg/dL, 0.6 pmol/L, and 0.5 pmol/L, respectively. Lyophilized quality control materials (Lyphochek Immunoassay Plus Control, Bio-Rad Laboratories) in three different concentrations were used to monitor accuracy of measurements. The intra- and inter-assay coefficients of variation (CVs) were respectively 2.8% and 3.1%.for TSH, 2.3% and 3.0% for T3, 1.7% and 2.6% for T4, 2.1% and 3.9% for FT3, and 1.0% and 2.9% for FT4. Mean values and the reference ranges of thyroid hormones obtained from the Tehran Thyroid Study (TTS) were TSH (1.77 ± 1.24; 0.32–5.06 mU/L) and FT4 (1.19 ± 0.16; 0.91–1.55 ng/dl) [