Results showed that the AUC of the ROC curve was 0.774 for IL-6 (P < 0.001), the optimal cut-off value for IL-6 concentration was 6.735 pg/mL, and the sensitivity and specificity to predict the severity of COVID-19 were 76.7% and 76.6%, respectively (Figure S2). Here, IL6 is linked to COVID-19.