RT Journal Article SR Electronic T1 C3a and C5b-9 levels differentially predict COVID-19 severity and mortality. JF European Respiratory Journal JO Eur Respir J FD European Respiratory Society SP 2093 DO 10.1183/13993003.congress-2022.2093 VO 60 IS suppl 66 A1 M Detsika A1 E Diamanti A1 K Ampelakiotou A1 E Jahaj A1 S Tsipilis A1 N Athanasiou A1 A Zacharis A1 I Dimopoulou A1 S Orfanos A1 A Tsirogianni A1 A Kotanidou YR 2022 UL http://erj.ersjournals.com/content/60/suppl_66/2093.abstract AB Introduction: SARS-COV-2 infection may result in pneumonia leading to ARDS and ICU treatment. Activation of the complement system was verified in COVID-19 patients as a driving factor of thromboinflammation contributing to disease progression.Aim: To investigate C3a and C5b-9 levels as markers of COVID-19 severity and outcome.Methods: 79 patients with a positive polymerase chain reaction (PCR) test for SARS-COV-2 were recruited; 38 severe and 42 critical. Serum samples were collected on admission and analysed for C3a and C5b-9 levels by ELISA methodology. Patients were grouped into severe vs critical, non-intubated vs intubated and survivors vs non-survivors for comparisons. Statistical analysis by Mann-Whitney for non-parametric analysis and receiving operating curve (ROC) analysis was performed in GraphPad Prism.Results: A statistically significant increase for C3a and C5b-9 levels was observed between: a) severe vs critical (p<0.001 and p<0.0001), b) non-intubated vs intubated (p<0.001 and p<0.05) survivors vs non-survivors (p<0.001 and p<0.01). ROC analysis for ICU admission revealed a higher AUC for C5b-9 (0.771, p<0.001) compared to C3a (AUC= 0.686, p<0.01). A higher AUC was observed for C3a when analysis was performed for intubation need (AUC=0.746, p<0.001) or mortality (AUC=0.758, p<0.0001) compared to C5b-9 (intubation need AUC=0.663, p<0.05 and mortality AUC=0.637, p NS). Combining C3a and C5b9 revealed a powerful prediction tool for ICU admission (AUC=0.773, p<0.0001), intubation (AUC=0.756, p<0.0001) and mortality (AUC=0.753, p<0.001).Conclusion: C3a and C5b-9 may serve as prognostic tools either separately or in combination for the progression and outcome of COVID-19.FootnotesCite this article as Eur Respir J 2022; 60: Suppl. 66, 2093.This article was presented at the 2022 ERS International Congress, in session “-”.This is an ERS International Congress abstract. No full-text version is available. Further material to accompany this abstract may be available at www.ers-education.org (ERS member access only).