ALT is released into the bloodstream when liver cells are damaged, making it a sensitive and relatively specific marker of liver injury. Elevations occur in viral hepatitis, fatty liver disease, alcohol-related liver damage, medication-induced injury, and many other liver conditions.
This test is part of standard liver panels and is also used to monitor patients on medications known to affect the liver, follow chronic hepatitis B or C, and evaluate unexplained fatigue or abnormal liver imaging. ALT is often interpreted alongside AST: the ratio between them and the magnitude of elevation help narrow the likely cause. Sample type is serum.