Diagnostic Performance of Fractional Excretion of Urea in Acute Kidney Injury in Patients With Liver Cirrhosis

Acute kidney injury (AKI) is a common complication of end-stage liver disease and is one of the criteria that define acute-on-chronic liver failure.

There are two types of AKI in cirrhosis: functional and structural. The functional group is divided into the volume responsive prerenal azotemia (PRA) that results from decreases in intravascular volume (e.g., aggressive diuretic treatment, diarrhea) and volume-unresponsive state or called hepatorenal syndrome (HRS). AKI that is unresponsive to albumin infusion and withdrawal of diuretics in the absence of identifiable causes. The structural group includes acute tubular necrosis (ATN) that results from intrinsic damage and other renal parenchymal disorders.

Urea is filtered in the glomerulus and then largely reabsorbed in the proximal tubule and also in the distal tubule. The reabsorption of urea is increased by vasopressin and the renin-angiotensin-aldosterone system. The fractional excretion of urea under conditions of decreased renal perfusion and increased vasopressin and renin-angiotensin-aldosterone system (RAAS), such as that seen in cirrhosis with PRA or HRS type 1, should therefore decrease. Conversely, renal tubular injury should impair reabsorption and increase its fractional excretion. Since urea absorption is largely modulated in the proximal tubules, it is not affected by diuretics acting more distally. Recently it is therefore hypothesized that the fractional excretion of urea (FEUrea) could serve as a clinical aid in making an early distinction between ATN versus PRA and HRS type 1 in patients with cirrhosis and ascites presenting with AKI. The current study was designed to test this hypothesis.