Statistics Quantitative data are expressed as mean ± SD. Differences between groups were assessed by two-tailed unpaired t-test. The relationship between variables was assessed by linear regression analysis. In order to allow statistical analysis the value of undetectable serum Tg expressed as < 0.2 ng/nL was arbitrarily changed in 0.10 ng/mL. Statistical significance was defined by a p-value < 0.05.