ALT Blood Test Test

The ALT blood test measures the amount of ALT (alanine transaminase) in your blood. ALT is an enzyme found mainly in your liver. When liver cells are damaged, they release ALT into your blood. High levels may indicate liver injury or disease. This test is often part of a routine screening or a group of liver function tests to check liver health.

What this test measures

An ALT test measures the amount of ALT in your blood. ALT is an enzyme found mainly in your liver. Usually, you have low levels of ALT in your blood, but when liver cells are damaged, they release ALT into the bloodstream.

What your results mean

Reference ranges vary by laboratory and by your age and sex. MedlinePlus does not publish a single normal range for this test — always read your result against the range printed on your own lab report and discuss it with your provider.

Higher-than-normal results

Higher-than-usual levels of ALT in your blood may be a sign of liver damage from hepatitis, infection, cirrhosis, liver cancer, other liver diseases, lack of blood flow to the liver, certain medicines, or poisons.

Lower-than-normal results

Lower-than-usual levels of ALT in your blood are not common. Your provider may do more tests since this may be a sign of B6 deficiency or chronic kidney disease.

Frequently asked questions

What does ALT stand for?

ALT stands for alanine transaminase, also called alanine aminotransferase.

Why is an ALT test done?

An ALT test is often part of a routine blood screening to check the health of your liver. It may also help diagnose or monitor liver problems.

What can cause high ALT levels?

High ALT levels may be caused by hepatitis, infection, cirrhosis, liver cancer, other liver diseases, lack of blood flow to the liver, certain medicines, or poisons.

What can cause low ALT levels?

Low ALT levels are not common but may be a sign of B6 deficiency or chronic kidney disease.

Can other factors affect ALT results?

Yes, many things can affect your results, such as your age, sex, weight, certain medicines and dietary supplements, intense exercise, and where you are in your menstrual cycle.

Sources

MedlinePlus: ALT Blood Test — NIH MedlinePlus

Last updated July 7, 2026. Information is aggregated from official public sources and is not a substitute for professional medical care.