ALT (alanine aminotransferase) is an enzyme found primarily in liver cells. When liver cells are damaged or inflamed, ALT leaks into the bloodstream, causing elevated blood levels. ALT is considered more specific to the liver than AST, which is also found in heart, muscle, and kidney tissue.

Mildly elevated ALT is extremely common and often reflects non-alcoholic fatty liver disease (NAFLD), which affects roughly 25% of adults. Other causes include medications (statins, acetaminophen), alcohol, viral hepatitis, autoimmune conditions, and intense exercise.

For health optimization, some researchers and clinicians argue that the standard lab reference ranges for ALT are set too high, as they were derived from populations that include people with undiagnosed liver disease. Many functional medicine practitioners consider optimal ALT to be below 25 IU/L for men and below 20 IU/L for women.

What It Measures

ALT measures the activity of alanine aminotransferase enzyme in the blood. Elevated levels indicate liver cell damage, as ALT is released when hepatocytes are injured.

Reference Ranges

How GATOR Tracks This

Related Biomarkers