2.4. Functional assessment of complement activation

Plasma was isolated from EDTA tubes collected at hospitalization for non‐ICU patients or at ICU admission for ICU patients and stored immediately at −80⁰C. Taking into account the difficulties of functional complement assessment in clinical laboratories, 41 we studied markers that would be potentially accessible in everyday clinical practice or the setting of a clinical trial. Therefore, we measured THBD (R&D, Bio‐Techne), C3a (Invitrogen, Thermo Fisher Scientific) and C5a (Affymetrix, Bender Medsystems) using commercially available ELISA assays. Statistical comparison of continuous variables between groups was performed using the statistical program SPSS 23.0 (IBM SPSS Statistics for Windows, Version 23.0.; IBM Corp). Descriptive statistics were described using median (interquartile range) or mean ±standard deviation for continuous variables according to normality, and frequency for categorical variables. Continuous variables were compared using t test or Mann‐Whitney, according to normality.