CALCA and bacterial infectious disease: Table 4 shows the evaluation of AUC, sensitivity, specificity, negative predictive value, positive predictive value, and the Youden index. These cut-off values were calculated based on the best sensitivity and specificity (Youden index), which were found to have the highest diagnostic value for predicting bacterial infections.  Figure 2(f) shows that of the inflammatory markers, PCT was the best predictor, with an AUC of 0.874 (95% CI 0.813–0.935), followed by CRP, with an AUC of 0.855 (95% CI 0.790–0.919).