Definition and Diagnosis of Acute Kidney Injury in Cirrhosis

<b><i>Background:</i></b> Acute kidney injury (AKI) is a common complication of advanced cirrhosis. Type 1 hepatorenal syndrome is the best-known and most severe form of AKI, and it has a precise definition and a set of specific diagnostic criteria. More recently, it has become recognized that milder degrees of renal dysfunction also have a negative impact on patient outcome in various patient populations. <b><i>Key Messages:</i></b> Several definitions and criteria for staging the severity of AKI have been proposed, including the RIFLE (Risk, Injury, Failure, Loss of Function and End-Stage Renal Disease) group, the Acute Kidney Injury Network (AKIN), and the Kidney Disease: Improving Global Outcome (KDIGO) group. All of them incorporate some changes of serum creatinine and urine output in the definition and staging of AKI. The hepatology community has mostly embraced the AKIN diagnostic and staging criteria and has applied them in the prognostication of patients with advanced cirrhosis. However, the AKIN criteria have not been strictly applied in all studies on cirrhosis. This is partly related to the fact that changes in urine output are difficult to assess in advanced cirrhosis, and partly related to the difficulty in defining the baseline serum creatinine from which the change in serum creatinine is calculated. This has led to some confusion in the interpretation of results of the various studies on AKI in cirrhosis. More recently, some investigators have suggested incorporating the AKIN criteria with setting a lower limit of serum creatinine of 1.5 mg/dl in determining the diagnosis and prognosis of AKI in cirrhosis. <b><i>Conclusions:</i></b> This is an ongoing debate as to how best to define AKI in cirrhosis. In the near future there should be prospective clinical trials that will clarify which diagnostic and staging criteria of AKI will best serve the cirrhotic population.