KLRG1 and COVID-19: ROC curve analysis (Figure 8A) demonstrated that CCR5 (AUC = 0.916), CYSLTR1 (AUC = 0.885), and KLRG1 (AUC = 0.899) exhibit superior diagnostic performance in distinguishing COVID-19 ICU patients from non-ICU patients compared to conventional clinical indicators such as C-reactive protein (CRP, AUC = 0.612), SOFA score (AUC = 0.607), APACHE II score (AUC = 0.557), and D-dimer levels (AUC = 0.848).