AST is alanine aminotransferase and ALT is alanine aminotransferase, which are laboratory markers for the diagnosis of liver diseases, and low levels of both are usually of little pathological significance. 1. The liver is rich in enzymes, and AST and ALT are the commonly used aminotransferases for checking liver function. 2. In hepatocytes, most of the aminotransferases are found in mitochondria and most of the aminotransferases are found in non-mitochondria, and their levels in the serum are normally very low. Therefore, low levels of AAT and ALT are not clinicopathologically significant. 3. However, when hepatocytes are damaged, AAT and ALT can be released into the plasma, resulting in elevated serum levels. Elevated levels of these two enzymes are therefore a cause for alarm and are usually indicative of liver disease.