Fractional Excretion of Urea: an Excellent Simple Tool for the Differential Diagnosis of Acute Kidney Injury in Liver Cirrhosis

AKI according to KDIGO guidelines is defined as the followings:

• An increase in serum creatinine by ≥0.3 mg/dl (≥26.5 µmol/l) within 48 h
• An increase in serum creatinine to ≥1.5 times baseline within the previous 7 days
• Urine volume ≤0.5 ml/kg/h for 6 h Serum creatinine overestimates renal function in cirrhotic patients due to a number of factors: Creatinine production in patients with cirrhosis is reduced due to muscle wasting, there is an increased secretion of creatinine in the renal tubules, sCr may be diluted due to an increased volume of distribution, and finally, high bilirubin levels may interfere with the assays to measure its level. Recently, the International Club of Ascites (ICA) has adopted the concept of AKI which was developed originally to be used in general critically-ill patients. AKI is defined as the increase of at least 0.3 mg/dL (26 μmol/L) and/or ≥ 50% from baseline, within 48 hours Since urea absorption is largely modulated in the proximal tubules, it is not affected by diuretics acting more distally. The investigators therefore hypothesized that the fractional excretion of urea (FEUrea) could serve as a clinical aid in making an early distinction between ATN versus Pre renal azotemia and HRS type 1 in patients with cirrhosis and ascites presenting with AKI Fractional excretion of urea (FEUrea) ([urine urea nitrogen/ blood urea nitrogen)/(urine creatinine/plasma creatinine)] X 100) < 35% is specific for prerenal azotemia, and > 50% is specific for ATN