Figure 2 showed the comparisons of AUCs for all independent factors of AKI in patients with CAP. The maximum AUC was reported for serum Cystatin C within 24 h after admission. Table 3 presented the accuracy of serum Cystatin C for detecting AKI in patients with CAP. Serum Cystatin C had an AUC of 0.81 (95% CI: 0.79–0.83, p < 0.001) for predicting AKI, with an optimal cutoff value of 1.37 mg/L, computing 68% sensitivity, 80% specificity, 57% positive predictive value and 86% negative predictive value. This evidence concerns the gene CST3 and acute kidney injury.