Fractional excretion of urea: A simple tool for the differential diagnosis of acute kidney injury in cirrhosis

ABSTRACT

Current approaches to determine the cause of acute kidney injury (AKI) in patients with cirrhosis are suboptimal. The aim of this study was to determine the utility of fractional excretion of urea (FEUrea) for the differential diagnosis of AKI in cirrhotic patients. A retrospective analysis was performed in patients (n=50) with cirrhosis and ascites admitted with AKI. Using adjudicated etiology assessment as the reference standard, receiver operating curves (ROC) and optimal cutoff, sensitivity (Sn) and specificity (Sp) for the diagnosis of prerenal azotemia (PRA), type 1 hepatorenal syndrome (HRS) and acute tubular necrosis (ATN) was derived. Validation was performed in an independent cohort (n=50) and by bootstrap analysis. The causes of AKI (derivation:validation cohorts) were: PRA 21:21, HRS 18:15, ATN: 11:14. Median FEUrea were statistically different across all etiologies of AKI in the derivation cohort (PRA 30.1 vs HRS 20.2 vs ATN 43.6, p=<0.001) and validation cohort (PRA 23.1 vs HRS 13.3 vs ATN 44.7, p=<0.001). The AUC (cutoff, Sn/Sp) for FEUrea was 0.96 (33.4, 85/100) for ATN vs non-ATN, 0.87 (28.7, 75/83) for HRS vs non-HRS, and 0.81 (21.6, 90/61) for PRA vs HRS. When applied to the validation cohort, the Sn/Sp were maintained for ATN vs non-ATN (93/97), HRS vs non-HRS (100/63), and for PRA vs HRS (67/80). After bootstrapping, the Sn/Sp for FEUrea in the ATN vs non-ATN, HRS vs non-HRS, and PRA vs HRS was 88/96, 63/97, and 55/87 respectively. Conclusions: FEUrea is a promising tool for the differential diagnosis of AKI in patients with cirrhosis. This article is protected by copyright. All rights reserved.

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