AST and ALT are proteins that are made in the liver cells. Small amounts leak out and can be measured in the blood. When liver cells are damaged, more proteins are released into the blood. In general, the ALT is higher than the AST, except in alcohol-related liver disease and when patients already have cirrhosis.


The purple ribbon-like structure on the left is what AST might look like and the aqua ribbon-like structure on the right is what the ALT protein might look like.

Learning points:

When AST and ALT are very high over 200, liver injury is happening pretty quickly
Normal ALT for men is 30 and under
Normal ALT for women is 19 and under

Exceptions:


AST and ALT may change quickly from low to very high levels in some people
Some diseases cause liver injury even when the AST and ALT are low or normal
AST and ALT may be high from other causes, such as severe muscle breakdown