The major allele A and AA genotype in SELENOP rs6865453, the major allele C and CC genotype in rs713041, the major allele G and GG genotype in rs2074451, and the major allele C and CC genotype in rs3746165 of GPX4 gene decreased in both GD and HT patients than those in the control. This evidence concerns the gene SELENOP and hematocrit.