Obstructive Sleep Apnoea and C-reactive protein levels: Data from the ESADA

<bold>Introduction:</bold> Obstructive Sleep Apnoea (OSA) characterized by intermittent hypoxia promotes systemic inflammation. This study aimed to evaluate the association between OSA and C-reactive protein (CRP) levels as marker of systemic inflammation in a large European patient cohort. <bold>Methods:</bold> This is a cross-sectional analysis of the multi-centre European Sleep Apnoea Database (ESADA, an ERS supported CRC) cohort. Inverse probability weighted regression adjustment for multiple covariates within a linear mixed - effects model (LMEM) was used to test the independent association between OSA severity and CRP levels. Covariates included anthropometrics and comorbidities. Study centre and year of study were considered to account for variability in CRP analysis methodologies. <bold>Results:</bold> 18,445 subjects (71 % male, median age 53 (interquartile range: [44; 62]) years, median AHI 22.1 [9; 44.9] events/h) were included. CRP (median 3.0 [1.2; 5.1] mg/L) increased in a dose-response fashion across OSA severity categories (2.0 [1.0;4.0] for AHI<5/h; 2.5 [1.0; 5.0] for AHI 5≤15/h); 2.9 [1.2; 5.0] for AHI 15-<30/h; and 3.7 [1.8, 6.4] mg/L for AHI ≥30/h, p<0.001, respectively). In the fully adjusted LMEM model, patients with an AHI≥30/h or the highest quartile of ODI/Time below SaO2<90% showed an elevated CRP level by 0.6 (95%CI 0.4-0.8), 0.8 (0.6, 1.0) and 0.9 (0.7, 1.1) mg/L, respectively, p<0.001. Severe obesity (BMI ≥35kgm2) was associated with elevated CRP levels by 2.7 (2.45, 2.90) mg/l. <bold>Conclusions:</bold> We demonstrate a robust dose-response relationship between OSA severity measures and systemic inflammation. Future studies should address if elevated CRP could serve as prognostic marker for subsequent cardiovascular events in OSA.