Acute liver failure may be classified on the basis of the time interval between the onset of symptoms and the development of encephalopathy as hyperacute, acute, subacute, fulminant, subfulminant and late-onset. The different classification systems used are O’Grady system, Bernuau system, and Japanese system. This classification based on time duration provides helpful clues about etiology, complications, and prognosis such as in hyperacute cases, the cause is usually viral infections or acetaminophen toxicity. The subacute cases can be due to idiosyncratic drug reactions and can also be confused with chronic liver disease. The hyperacute liver failure has a better prognosis than subacute liver failure.

Acute liver failure may be classified on the basis of the duration of the symptoms between the onset of jaundice to the onset of encephalopathy. The different classification systems based on the number of weeks from the appearance of jaundice to the encephalopathy are:^{[1][2][3][4][5][6]}

• This classification based on time duration provides helpful clues about etiology, complications, and prognosis such as in hyperacute cases, the cause is usually viral infections or acetaminophen toxicity.
• The subacute cases can be due to idiosyncratic drug reactions and can also be confused with chronic liver disease.
• The hyperacute liver failure has a better prognosis than subacute liver failure.

There is no established classification of acute liver failure on the basis of etiology. However, it can be classified on the basis of etiology as:^[7][8]

• The viruses associated with hepatitis are hepatitis A, B, C, D, E, cytomegalovirus (CMV), varicella, herpes simplex virus (HSV) and adenovirus.

• Hemochromatosis
• Wilson’s disease

• Righ heart failure
• Portal vein thrombosis
• Budd chiari syndrome

• Acetaminopehn
• Carbontetrachloride (CCL4)
• Isonizid (INH)
• Halothane
• Valproic acid
• Amanita phalloides

• HELLP syndrome
• Acute fatty liver of pregnancy
• Reye’s syndrome