Fig. 3

ROC curve analysis using KL-6, RSG and combined score for predicting the 28-day mortality, and Kaplan-Meier curves of 28-day survival in patients according to binary risk group stratification. (1) KL-6 yielded an AUC of 0.885 (95% CI: 0.804–0.952), while RSG yielded an AUC of 0.818 (95% CI: 0.711–0.899). The combined score in both development group and validation group yielded AUCs of 0.868 (95% CI: 0.776–0.942) and 0.932 (95% CI: 0.862–0.997), respectively. (2) K-P curve of KL-6 (low risk: <810 U/ml; high risk: ≥ 810 U/ml), (3) K-P curve of RSG (low risk: <3; high risk: ≥3), (4) K-P curve of combined score in the development group (low risk: < 103.04; high risk: ≥ 103.04), (5) K-P curve of combined score in the validation group (low risk: < 103.04; high risk: ≥103.04). KL6 Krebs von den Lungen-6, RSG radiological severity grade, K-P Kaplan-Meier