The ALT (Alanine Aminotransferase) test is one of the components of the Liver Health Panel. ALT (Alanine Aminotransferase) which used to be called SGTP is an enzyme found mostly in the liver; smaller amounts of it are also in the kidneys, heart, and muscles. Under normal conditions, ALT levels in the blood are low. When the liver is damaged, ALT is released into the blood stream, usually before more obvious symptoms of liver damage occur, such as jaundice (yellowing of the eyes and skin).The ALT test detects liver injury. ALT values are usually compared to the levels of other enzymes, such as alkaline phosphatase ( ALP) and aspartate aminotransferase ( AST) to help determine which form of liver disease is present..