Fig. 4

shows the ROC curve according to 1) readmission duration, 2) DNI, 3) readmission duration + DNI, and 4) readmission duration + CAP. AUC for readmission duration (≤ 30 d) + DNI level (≥ 3.5%) is 0.753 (95% CI 0.676–0.830, P < 0.001) with a sensitivity of 73.7% and a specificity of 67.3%; AUC for readmission duration + CAP 0.678 (95% CI 0.597–0.758), readmission duration 0.677 (95% CI 0.590–0.765), and DNI 0.654 (95% 0.573–0.735), respectively. AUC = area under the curve; CAP = community-acquired pneumonia; DNI = delta neutrophil index; d = days; ROC = receiver operating characteristic