CFS patients notably exhibited relatively lower FT3, TT4, and TT3; lower deiodination function (SPINA-GD), lower thyroid secretory function (SPINA-GT), lower protein binding of thyroid hormones (TT3/FT3, TT4/FT4), and lower T3/T4 hormone ratios (TT3/TT4, FT3/FT4), lower %TT3, higher %rT3, and higher rT3/TT3 ratio. Here, PAEP is linked to myalgic encephalomeyelitis/chronic fatigue syndrome.