Moreover, we found that the CAT score combined with home oxygen therapy and CD4+CD8+ T cells% to predict respiratory failure in AECOPD patients were the best (AUC = 0.77, 95% CI: 0.70–0.86, P < 0.0001, sensitivity: 60.4%, specificity: 86.8%) (Fig. 4). Here, CD4 is linked to respiratory failure.