Fig. 4 TSS for diagnosing severe-critical COVID-19. Using ROC to test the differential diagnosis ability of TSS in common-type group and severe-critical-type group. ROC analysis showed the area under the curve (AUC) of TSS for diagnosing severe-critical type was 0.918 (95%CI 0.843–0.994). The TSS cutoff of 7.5 had 82.6% sensitivity and 100% specificity