Muscle sources of the enzymes, such as intense exercise, are unrelated to liver function and can markedly increase AST and ALT.

The liver has transaminases to synthesize and break down amino acids and to convert energy storage molecules.

[citation needed] Measurement of ALT and AST were used in diagnosing heart attacks, although they have been replaced by newer enzyme and protein tests that are more specific for cardiac damage.

[citation needed] Possible causes for high ALT levels are liver inflammation (hepatitis A, B, C, infectious mononucleosis, acute viral fever, alcohol, pancreatic disorder), injury to muscles (trauma, myocardial infarction, congestive heart failure, acute kidney failure), and many toxins and drugs.

[5] The magnitude of AST and ALT elevations vary depending on the cause of the increase, such as intensity of recent muscular exertion or type of hepatocellular injury.