In the OSA group, compared with the middle and highest tertile of the FT3/FT4 ratio, patients in the lowest tertile of the FT3/FT4 ratio were more likely to be female, to have a history of stroke, to be current smokers, and to have lower blood pressure, LVEF, eGFR, total cholesterol, low-density lipoprotein, but higher BNP, hemoglobin A1C and Hs-CRP. Here, CRP is linked to obstructive sleep apnea syndrome.