Definition of Acute Liver Failure
Acute liver failure (ALF) is defined as evidence of coagulation abnormality (INR ≥ 1.5) and any degree of mental alteration (encephalopathy) in a patient without preexisting cirrhosis and with an illness duration of ≤26 weeks 1.
Core Diagnostic Criteria
The widely accepted definition requires three essential components:
- Coagulopathy: INR ≥ 1.5 (or prothrombin time prolonged by 4-6 seconds or more)
- Hepatic encephalopathy: Any degree of mental alteration
- Absence of preexisting cirrhosis: Patient must not have known chronic liver disease
- Time frame: Illness duration ≤26 weeks from symptom onset 1
Important Exceptions and Caveats
Three specific conditions may be included even if cirrhosis is present, provided the disease has only been recognized for ≤26 weeks 1:
- Wilson disease
- Vertically-acquired hepatitis B virus
- Autoimmune hepatitis
This exception exists because these patients may have unrecognized cirrhosis at presentation but still follow the clinical trajectory of ALF.
Terminology Clarification
The term "acute liver failure" is preferred over older terminology such as "fulminant hepatic failure" or "fulminant hepatitis" 1. Subcategorizations based on illness duration (hyperacute: <7 days, acute: 7-21 days, subacute: 21 days to 26 weeks) are not particularly helpful since they lack prognostic significance independent of the underlying cause 1. For example, hyperacute cases may appear to have better prognosis, but this is primarily because most are due to acetaminophen toxicity rather than the time course itself.
Critical Distinction from Acute-on-Chronic Liver Failure
ALF must be distinguished from acute-on-chronic liver failure (ACLF), which occurs in patients with known chronic liver disease or cirrhosis 2. This distinction is crucial because prognostic criteria and management strategies differ significantly between these two entities 1.
Clinical Recognition
When evaluating a patient with acute hepatitis, immediate measurement of prothrombin time and careful evaluation for subtle alterations in mentation are mandatory 1. If both coagulopathy (INR ≥1.5) and any evidence of altered sensorium are present, the diagnosis of ALF is established and hospital admission is mandatory, with early ICU transfer preferred given the potential for rapid hour-by-hour deterioration 1.