For diagnosis of the critical COVID-19, the area under ROC curve of IL-6 was the largest among all cytokines; the preoperative IL-6 concentration of 9.16 pg/ml was the optimal cutoff value (sensitivity = 82.4 (56.6–96.0)%, specificity = 78.5 (70.4–985.2)%), the positive predictive values = 33.3(19.6–49.5)%, the negative predictive values = 97.1(91.1–99.4)% (Figure 7 and Supplementary Table 7). Here, IL6 is linked to COVID-19.