What Is ALT in a Blood Test?

ALT stands for Alanine Aminotransferase, an enzyme found mainly in liver cells. When liver cells are damaged or inflamed, ALT leaks into the bloodstream, making it a key marker for liver health. ALT is measured as part of a Comprehensive Metabolic Panel (CMP) or liver function panel. It is also sometimes called SGPT (serum glutamic-pyruvic transaminase).

Normal Range

• Adult normal: 7–56 U/L (units per liter), though ranges vary by laboratory.
• Mild elevation: 1–3× upper limit of normal.
• Moderate to marked elevation: more than 3× the upper limit.

What Causes Elevated ALT?

• Non-alcoholic fatty liver disease (NAFLD) — the most common cause of mild ALT elevations in the U.S.
• Hepatitis B or C — viral liver infections causing moderate to marked elevations.
• Alcohol-related liver disease — chronic heavy drinking damages liver cells.
• Medications — acetaminophen overdose, statins, certain antibiotics, and anti-seizure drugs.
• Hemochromatosis — iron overload.
• Autoimmune hepatitis — immune-mediated liver inflammation.

When Is ALT Concerning?

A single mildly elevated ALT is not necessarily cause for alarm. Temporary elevations can follow vigorous exercise, a recent viral illness, or even a fatty meal before the blood draw. Persistent elevations or values above twice normal should be investigated with repeat testing, AST, GGT, and possibly imaging (ultrasound) to evaluate for fatty liver or structural liver disease.