Plasma renalase as a biomarker of acute kidney injury after cardiac surgery

Background Renal ischemia/reperfusion injury is a major cause of acute renal failure. The lack of validated early biomarkers for predicting acute kidney injury (AKI) has hampered our ability to initiate potentially preventive and therapeutic measures in an opportune way. We tested the hypothesis that plasma renalase is an early biomarker for ischemic renal injury after cardiac surgery. Patients and methods We prospectively evaluated 40 adult patients who underwent cardiac surgery. Patients were divided into the AKI group and the non-AKI group on the basis of whether they developed postoperative AKI within 48 h after surgery. Plasma renalase levels were measured before surgery and 24 h after surgery. The primary outcome was AKI diagnosed using the Acute Kidney Injury Network criteria. Results Twenty-five (62.5%) patients developed AKI after surgery. Plasma renalase decreased significantly from a mean of 1.2±0.46 ng/ml at baseline to 0.9±0.42 ng/ml 24 h after cardiopulmonary bypass, with a mean %change of 27±14.8 in the AKI group. Univariate analysis showed a significant correlation between AKI and the following: %change in plasma renalase, cardiopulmonary bypass time, and aortic cross-clamp time. Receiver operating characteristic curve analysis revealed that for %change in plasma renalase concentrations at 24 h, the area under the curve was 0 · 9, sensitivity was 0.92, specificity was 0 · 87, and likelihood ratio was 7.07 for a cutoff value of 9% change. Conclusion Plasma renalase %change is more valid compared with renalase before or after procedure and neutrophil gelatinase-associated lipocalin in the prediction of AKI and represents a novel and highly predictive early biomarker for AKI after cardiac surgery.