<![CDATA[Background: Cardiac surgery using a cardiopulmonary bypass (CPB) machine is a complex procedure that can trigger systemic inflammatory responses, tissue perfusion disorders, and lactate accumulation. Cardiac surgery-associated acute kidney injury (CSA-AKI) is a serious postoperative complication of cardiac surgery that increases morbidity, mortality, and duration of intensive care unit (ICU) stay.Objective: This study aims to determine the relationship between lactate concentration and the incidence of CSA-AKI and to establish the lactate cut-off value as a risk marker for CSA-AKI in patients following cardiac surgery using a cardiopulmonary bypass machine at Dr. Sardjito General Hospital Yogyakarta.Methods: A prospective cohort study (December 2025--February 2026) on elective cardiac surgery patients at Dr. Sardjito General Hospital. Inclusion criteria: age ≥18 years, NYHA <class III, and eGFR ≥60 mL/min/1.73 m². CSA-AKI was defined based on KDIGO 2012 criteria.Results: Study subjects comprised 43 subjects (from a total of 45 patients, 2 dropouts). Mean age 46.84 ± 12.40 years, male (60.5%), EF 61.97 ± 9.17%. Procedures were dominated by CABG (37.2%) and valve surgery (37.2%), with CPB duration 96.13 ± 23.71 minutes. The incidence of CSA-AKI was 65.1%. ROC curve analysis of lactate 6 hours post-CPB showed AUC 0.800 (p=0.001) with optimal cut-off 3.44 mmol/L (sensitivity 71.4%, specificity 73.3%)Conclusion: There is a positive relationship between lactate concentration 6 hours post-CPB and the incidence of CSA-AKI, and lactate cut-off value 6 hours post-CPB ≥3.44 mmol/L has potential as a risk marker for CSA-AKI in patients following cardiac surgery with a cardiopulmonary]]>
