The numbers of CD3+ T cells (area under curve (AUC) =0.980), CD4+ T cells (AUC=0.972), and CD8+ T cells (AUC=0.933) provided a diagnostic value by identifying severe COVID-19 patients with high sensitivity and specificity, of whom the cut-off values were 575, 392, 214 cells/μL, respectively [21]. Here, CD4 is linked to COVID-19.