['Oxidative stress is a typical feature of obstructive sleep apnea (OSA). Thioredoxin (TRX), as one of the oxidative stress biomarkers, is a potent protein disulfide reductase in antioxidant defense. Our study is designed to test whether thioredoxin could assess the severity of OSA.', 'Sixty-three adults suspected of having OSA were included in this study and were divided into four groups based on the results of polysomnography (PSG): control, mild, moderate, and severe. Subjects with chronic medical diseases (with the exception of essential hypertension) or taking any antioxidant medication were excluded. Blood samples were obtained within an hour after the overnight PSG test. Plasma TRX levels were detected by enzyme-linked immunosorbent assay.', 'The plasma TRX level in severe group was obviously increased (8.62\u2009±\u20092.14, 13.33\u2009±\u20095.60, 14.71\u2009±\u20095.53, and 16.10\u2009±\u20097.34 ng/ml; p\u2009<\u20090.05). The TRX positively related to AHI (r\u2009=\u20090.313; p\u2009<\u20090.05), while negatively related to the lowest O(2) saturation (r\u2009=\u20090.266; p\u2009<\u20090.037). The OSA patients associated with hypertension showed elevated TRX level (17.70\u2009±\u20096.98 vs. 13.43\u2009±\u20095.83 ng/ml; t\u2009=\u20092.434, p\u2009<\u20090.018). The cutoff value of TRX for identifying OSA was 9.39 ng/ml (sensitivity 91 %, specificity 78 %), and its cutoff value for differentiating moderate-severe OSA from mild OSA was 11.79 ng/ml (sensitivity 75 %, specificity 65 %).'] Are levels of thioredoxin related to the severity of obstructive sleep apnea : based on oxidative stress concept?