Alanine Transaminase (ALT)

Alanine transaminase (ALT) is used by your body to metabolize protein. If the liver is damaged or not functioning properly, ALT is released into the blood. This causes ALT levels to increase. A high result on this test can be a sign of liver damage. Normal ALT is between 21-71.

Aspartate Transaminase (AST)

Aspartate transaminase (AST) is an enzyme found in several parts of your body, including the heart, liver, and muscles. Since AST levels aren’t specific for liver damage, it’s usually measured together with ALT to check for liver problems. Your doctor may use an ALT-to-AST ratio to help with their diagnosis. When the liver is damaged, AST is released into the bloodstream. A high result on an AST test might indicate a problem with the liver or muscles. Normal AST is between 17-59.


It is important to note that if the liver is severely damaged, it may reach a point where it no longer releases the ALT/AST enzymes, and the tests may show normal. These tests are good for determining acute injury, but not for determining residual function. A patients AST/ALT may be declining, but this could be due to the liver reaching a point where production of these enzymes are not occurring, it does not necessarily mean that the liver is improving.

Causes For Abnormal Labs
  • Viral Hepatitis
  • Cirrhosis (from multiple conditions)
  • Liver damage from ETOH abuse
  • Acetaminophen
  • Statins
  • Seizure medications