Prognostic Value of Red Blood Cell Distribution Width in Predicting Acute Kidney Injury After Cardiac Surgery: A Retrospective Cohort Study

<b>Background/Objectives</b>: Acute kidney injury (AKI) remains a significant complication following cardiac surgery, associated with increased morbidity and mortality. The early detection of AKI is limited by the cost, availability, and unclear clinical utility of the current biomarkers. This study aimed to evaluate the red cell distribution width (RDW) on ICU admission as a predictor of postoperative AKI. <b>Methods</b>: We conducted a retrospective analysis of adult patients undergoing isolated coronary artery bypass grafting (CABG) or combined CABG and aortic valve surgery at a tertiary cardiac surgery centre (University Hospital of Siena, Italy) between January 2015 and December 2020. AKI was defined according to the KDIGO criteria. The RDW was measured preoperatively (T0), at ICU admission (T1), and at 24 (T2) and 48 h (T3) postoperatively. Temporal RDW changes (ΔRDW) were also calculated. Multivariate logistic regression identified independent predictors of AKI, and receiver operating characteristic (ROC) analysis evaluated the predictive accuracy. <b>Results</b>: A total of 456 patients were included, with an overall AKI incidence of 31%. Patients developing AKI exhibited significantly higher RDW at all measured time points, especially at ICU admission. Multivariate analysis identified age, RDW (OR 1.19, 95% CI: 1.03-1.37, <i>p</i> = 0.016) and serum creatinine at ICU admission, and elevated lactate at T2 as independent AKI predictors. In subgroup analyses, RDW at ICU admission remained significantly associated with AKI in patients who were not transfused, but not in patients who were. <b>Conclusions</b>: In this study, a high RDW at ICU admission represented an early postoperative marker independently associated with AKI after cardiac surgery, particularly in patients who did not receive transfusion.