Alanine Transaminase (ALT)

ALT is a liver enzyme and is measured to assess diseases of the liver.

Alanine Transaminase (ALT) Overview

Reviewed: April 21, 2014

Alanine transaminase is a liver enzyme involved in a number of chemical reactions important to the production of energy. ALT labs are useful in the diagnosis and management of certain liver diseases, as significant elevations of ALT occur only in diseases of the liver.

Lab values are reported in units per liter (U/L).

The normal range for ALT changes with age.

Male (U/L)

  • <1 Month 3-25
  • 1-11 Months 4-35
  • 1-3 Years 5-30
  • 4-12 Years 8-30
  • 13-15 Years 7-32
  • 16-19 Years 8-46
  • ≥20 Years 9-46

Female (U/L)

  • <1 Month 3-25
  • 1-11 Months 3-30
  • 1-3 Years 5-30
  • 4-12 Years 8-24
  • 13-15 Years 6-19
  • 16-19 Years 5-32
  • ≥20 Years 6-29


Blood draw


Fasting is not required before the test.

What the results mean

Higher than normal lab values found in blood samples often mean recent or ongoing liver damage as a result of hepatitis, diabetes, injury, or other reasons. A more specific cause of the damage can be found by comparing ALT with other liver tests. This damage is not always apparent on other tests including imaging procedures like X-rays and MRIs.