CST3 and acute kidney injury: There are some limitations of this study: (1) In a retrospective clinical study, there are no 90-day follow-up data for some patients, and some patients have incomplete preoperative detection indicators, such as cystatin C, hemoglobin A1c, and N-terminal-pro hormone BNP; however, these indicators were not included for univariate and multivariate analyses in this study and (2) Patients without AKI after cardiac surgery were not included for comparison to analyze the occurrence of CKD in this population.