Erythrocyte transfusion limits the role of elevated red cell distribution width on predicting cardiac surgery associated acute kidney injury

Background: Acute kidney injury (AKI) is one of the more serious complications after cardiac surgery. Elevated red cell distribution width (RDW) was reported as a predictor for cardiac surgery associated acute kidney injury (CSAKI). However, the increment of RDW by erythrocyte transfusion makes its prognostic role doubtful. The aim of this study is to elucidate the impact of erythrocyte transfusion on the prognostic role of elevated RDW for predicting CSAKI. Methods: A total of 3207 eligible patients who underwent cardiac surgery during 2016-2017 were enrolled. Changes of RDW was defined as the difference between preoperative RDW and RDW measured 24 h after cardiac surgery. The primary outcome was CSAKI which was defined by the Kidney Disease: Improving Global Outcomes Definition and Staging (KDIGO) criteria. Univariate and multivariate analysis were performed to identify predictors for CSAKI. Results: The incidence of CSAKI was 38.07% and the mortality was 1.18%. CSAKI patients had higher elevated RDW than those without CSAKI (0.65% vs. 0.39%, p < 0.001). Multivariate regression showed that male, age, New York Heat Association classification 3-4, elevated RDW, estimated glomerular filtration rate < 60 mL/min/1.73 m(2), cardiopulmonary bypass time > 120 min and erythrocyte transfusion were associated with CSAKI. Subgroup analysis showed elevated RDW was an independent predictor for CSAKI in the non-transfused subset (adjusted odds ratio: 1.616, p < 0.001) whereas no significant association between elevated RDW and CSAKI was found in the transfused patients (odds ratio: 1.040, p = 0.497). Conclusions: Elevated RDW is one of the independent predictors of CSAKI in the absence of erythrocyte transfusion, which limits the prognostic role of the former on predicting CSAKI.