Effect of Urine Output on the Predictive Precision of NephroCheck in On-Pump Cardiac Surgery with Crystalloid Cardioplegia: Insights from the PrevAKI Study

Object: Previous studies in other settings suggested that urine output (UO) might affect NephroCheck® predictive value. We investigated the correlation between NephroCheck® and UO in cardiac surgery patients.Design: Post-hoc analysis of a multicenter studySetting: University hospitalParticipants: Patients who underwent cardiac surgery utilizing cardiopulmonary bypass (CPB) and crystalloid cardioplegia.Measurements and Main Results: All patients underwent NephroCheck® testing four hours after CPB discontinuation. The primary outcome was the correlation between urine output, NephroCheck results, and acute kidney injury (AKI - defined according to Kidney Disease: Improving Global Outcome). Out of 354 patients, 337 were included. Median NephroCheck® values were 0.06 (ng/mL)2/1000) for the overall population and 0.15 (ng/mL)2/1000) for patients with moderate-to-severe AKI. NephroCheck® showed a significant inverse correlation with UO (ρ = -0.17, p=0.002) at the time of measurement. The area under the receiver characteristic curve (AUROC) for NephroCheck® was 0.60 (95% confidence interval [CI], 0.54 to 0.65) while for serum creatinine was 0.82 (95% CI: 0.78 to 0.86; p < 0.001). When limiting the analysis to the prediction of moderate-to-severe AKI, NephroCheck® had a AUROC of 0.82 (95% CI: 0.77 to 0.86; p<0.0001), while creatinine an AUROC of 0.83 (95% CI: 0.79 to 0.87; p=0.001).Conclusions: NephroCheck® measured four hours after the discontinuation from the CPB predicts moderate-to-severe AKI. However, a lower threshold may be necessary in patients undergoing cardiac surgery with CPB. Creatinine measured at the same time of the test remains a reliable marker of subsequent development of renal failure.