Acute kidney injury (AKI) is diagnosed by an increase in serum creatinine (SCr) ≥ 0.3 mg/dL within 48 hours or a ≥ 50% increase in SCr that is known or presumed to have occurred within the preceding 7 days. AKI in cirrhosis is mainly caused by prerenal AKI or acute tubular necrosis (ATN). The two main causes of prerenal AKI are hypovolemia and hepatorenal syndrome (HRS).

AKI commonly occurs in cirrhosis, and its causes must be evaluated before HRS is diagnosed. AKI must be differentiated from HRS. HRS, a type of AKI known as HRS-AKI under the current terminology, is unique to patients with cirrhosis and occurs in the absence of hypovolemia or significant abnormalities in kidney histology. HRS almost always occurs in patients with cirrhosis who also have ascites and hyponatremia, not compensated disease. Before the development of the new AKI criteria, patients with HRS were classified according to two clinical patterns. The first pattern, known as type-1 HRS, defined by an abrupt decline in kidney function, falls under the current criteria of AKI (100% increase in SCr to a value greater than 2.5 mg/dL). The second pattern, previously known as type-2 HRS, falls into the current definition of chronic kidney disease.