Alanine Aminotransferase (ALT/SGPT)

Alanine aminotransferase (ALT), also known as alanine transaminase or serum glutamic-pyruvic transaminase (SGPT), is used to detect and follow hepatocellular injury, including viral hepatitis and toxic or drug-induced hepatitis, and to aid in the assessment of cirrhosis and other liver disorders. ALT is commonly ordered with AST; the magnitude and pattern of ALT and AST elevations, and their ratio, can support differential diagnosis. In suspected acute hepatitis A or B and in hepatitis C, serologic assays establish the specific etiology. Persistent absence of viral hepatitis markers in the setting of hepatitic enzyme elevations may suggest drug-induced hepatitis that improves after the agent is withdrawn. ALT can also increase with infectious mononucleosis and may be elevated in heart failure.

ALT resides predominantly within hepatocytes. Hepatocellular injury increases membrane permeability or causes cell necrosis, permitting ALT to enter the circulation—often preceding clinical manifestations such as jaundice. ALT and AST are core components of routine liver panels; compared with AST, ALT is generally more specific for hepatocellular injury. When interpreted together, the AST/ALT ratio can help suggest potential etiologies of liver disease. Although ALT is primarily hepatic, elevations can occur with extrahepatic conditions, including disorders of skeletal muscle.