Transient versus persistent acute kidney injury and the diagnostic performance of fractional excretion of urea in critically ill patients

To evaluate the performance of fractional excretion of urea (FeU) for differentiating transient (T) from persistent (P) acute kidney injury (AKI) and to assess performance of FeU in predicting AKI in patients admitted to the ICU. We performed secondary analysis of a multicenter prospective observational cohort study on the predictive performance of biological markers for AKI in critically ill patients. AKI was diagnosed according to RIFLE staging. Of 150 patients, 51 and 41 patients were classified as having T-AKI and P-AKI, respectively. The diagnostic performance for FeU to discriminate T-AKI from P-AKI on the day of AKI was poor (AUC-ROC = 0.61; 95% CI: 0.49-0.73). The diagnostic performance of FeU to predict AKI 1 and 2 days prior to AKI was poor as well (AUC-ROC = 0.61; 95% CI: 0.47-0.74, and 0.58; 95% CI: 0.43-0.73, respectively). FeU does not seem to be helpful in differentiating T- from P-AKI in critically ill patients and it is a poor predictor of AKI