In assessing the relation between serum level of cystatin C with AKI, a significant heterogeneity was observed between the studies (I2 = 91.2%; p < 0.001) while minor heterogeneity was found in the second part of our analyses evaluating the urine concentration of cystatin C (I2 = 49.1%; p = 0.04). Here, CST3 is linked to acute kidney injury.