Interleukin (IL)-6 levels and severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) RNA copy number in plasma on admission, receiver operating characteristic (ROC) analysis for combined different variables, and Kaplan-Meier event-free survival analysis for a combined event of extracorporeal membrane oxygenation (ECMO) use and in-hospital death.

(A) IL-6 level and SARS-CoV-2 RNA copy number on admission were compared between COVID-19 patients with fatal outcomes including ECMO use and in-hospital death (Fatal group) and those without fatal outcomes (non-Fatal group). Closed circles indicate individual levels of IL-6 or SARS-CoV-2 RNA in plasma. The mean±SEM of IL-6 level and SARS-CoV-2 RNA copy number in non-Fatal and Fatal groups are as follows (IL-6: 60.9±16.3 pg/mL and 321.9±87.6 pg/mL, P < 0.0001, respectively; SARS-CoV-2 RNA: 0.5±0.2 copies/μL and 38.5±19.2 copies/μL, P < 0.0001, respectively). (B) ROC curves for combination of different variables on admission before intubation, including IL-6, SARS-CoV-2 RNA, and the ratio of oxygen saturation to fraction of inspired oxygen (SpO2/FiO2). (C) Kaplan-Meier curves showing incidence rate of a combined event of ECMO use and in-hospital death according to above or below optimal cutoffs of IL-6 level (49.0 pg/mL) and SARS-CoV-2 RNA copy number (1.5 copies/μL) in high-risk patients with low SpO2/FiO2 (< 261). Group 1: Both high IL-6 (> 49.0 pg/mL) and SARS-CoV-2 RNAaemia (> 1.5 copies/μL); Group 2: Either high IL-6 or SARS-CoV-2 RNAaemia; Group 3: Neither high IL-6 nor RNAemia of SARS-CoV-2.