What is the normal range for alanine aminotransferase (ALT)?

Under normal circumstances, alanine aminotransferase (ALT) is a key indicator in liver function tests, with a typical reference range of 0–40 U/L. Slight variations may occur depending on the assay method and laboratory.

ALT is predominantly located within hepatocytes. When hepatocytes are damaged, ALT is released into the bloodstream, leading to elevated serum ALT levels. Thus, measuring serum ALT concentration provides, to some extent, an indication of hepatocellular injury. Elevated ALT levels may suggest hepatic inflammation, toxicity, necrosis, or other pathological conditions—such as viral hepatitis, drug-induced liver injury, alcoholic liver disease, or nonalcoholic fatty liver disease (NAFLD). However, mild ALT elevation does not necessarily indicate severe liver disease; transient, modest increases can also result from intense physical exercise, excessive fatigue, sleep deprivation, alcohol consumption, or certain medications.

If abnormal ALT levels are detected, there is no need for undue alarm. A comprehensive assessment should be performed, integrating clinical symptoms, physical signs, and additional diagnostic test results. Furthermore, maintaining a healthy lifestyle supports normal liver function and helps stabilize ALT levels.