Serum Transferrin Level Is Associated with the Severity of Obstructive Sleep Apnea Independently of Obesity: A Propensity Score-Match Observational Study

INTRODUCTION: Dysregulation of iron metabolism is closely associated with the development of obesity and obstructive sleep apnea (OSA), but little is known about the relationship between serum transferrin (TF) level and OSA severity. We aimed to verify this relationship and fit into account for obesity-related confounders among bariatric candidates. METHODS: We compared data retrospectively collected in 270 bariatric candidates. A propensity score-matched (PSM) analysis was used to determine the impact of iron metabolism on OSA severity independently of obesity. Univariate analysis was used to evaluate the relationship between serum TF level and the severity of OSA reflected by hypoxia and night awakenings parameters. Serum TF level to predict the severity of OSA was assessed by using univariate and multiple logistic regression model. RESULTS: The preliminary analysis showed that serum ferritin (113 ng/mL [50–203] vs. 79 ng/mL [40–130], p = 0.009) and TF (2.72 g/L [2.46–3.09] vs. 2.65 g/L [2.34–2.93], p = 0.039) level was significantly higher in the moderate/severe OSA group than the no/mild OSA group. After PSM analysis, there were 75 patients in each group and only serum TF level remained significant (p = 0.014). The proportion of patients with combined T2D and hyperlipidemia also remained higher in moderate/severe OSA groups. Univariate analysis showed that the group with higher degree of hypoxia had higher serum TF levels no matter the severity of OSA was grouped by oxygen desaturation index (ODI; 2.79 g/L [2.56–3.06] vs. 2.55 g/L [2.22–2.84], p < 0.001) or minimum oxygen saturation (SpO₂nadir; 2.75 g/L [2.50–3.03] vs. 2.56 g/L [2.24–2.92], p = 0.009). Univariate and multiple logistic regression analysis further showed that serum TF level emerged as a significant and independent factor associated with OSA severity especially grouped by ODI (odds ratio: 2.91, 95% CI: 1.36–6.23, p = 0.006). CONCLUSION: The existence of OSA exacerbates obesity comorbidities, particularly type 2 diabetes and hyperlipidemia. Serum TF level is associated with the severity of OSA independently of obesity and might be a potential identification and therapeutic targets.