The two tests commonly called the "liver enzymes" are AST (aspartate transaminase or aspartate aminotransferase) and ALT (alanine transaminase or alanine aminotransferase).

The normal range for these tests varies from lab to lab. The high end of the range for each is around 40 U/L.

If liver cells are inflamed or damaged, the cells "leak" AST and ALT into the bloodstream. An elevated level can indicate liver damage.

Many things can cause your liver to become injured. Injuries large and small can cause AST and ALT changes. Some of the most common things to cause changes are:

• Alcohol
• Viral hepatitis
• Other viruses (such as mononucleosis)
• Many medications but particularly acetaminophen (Tylenol)
• Fatty liver from obesity or diabetes

As it turns out, AST and ALT are also present in a few other tissues, particularly in muscle. Muscle injury can also cause an increase of the AST and ALT blood level.