We evaluated whether a bedside endothelial activation index (EAI = D-dimer/fibrinogen) identifies biologically distinct phenotypes and relates to interleukin-6 (IL-6) response after therapeutic plasma exchange (TPE), and whether baseline IL-6 predicts a ≥50% IL-6 reduction.<h4>Methods</h4>Retrospective single-center ICU cohort of adults with SARS-CoV-2 infection, sepsis-related organ dysfunction, and ≥1 TPE session (n = 51). Here, IL6 is linked to Sepsis.