Elevated liver enzymes: Symptom — Overview covers definition, possible causes Alanine transaminase (ALT); Aspartate transaminase (AST). The London Clinic through its Liver Centre provides access to the latest developments in the diagnosis and treatment of liver disease and performs private ALT. An alanine aminotransferase (ALT) test measures the level of ALT in your blood. ALT is an enzyme made by cells in your liver. The liver is the.