ALT is alanine aminotransferase and AST is aspartate aminotransferase. These two enzymes mainly exist in hepatocytes. Therefore, when liver cells are damaged, ALT and AST will be released, and the indexes of two enzymes in serum will rise.

However, because ALT exists in cytoplasm and AST exists in mitochondria in cytoplasm, the increase of AST generally means severe liver injury, and ALT is more sensitive as a detection index for general liver injury and chronic hepatitis.