Reading a Chemistry, ALT

ALT is an enzyme that is found on the inside of liver cells.  So, when liver cells get damaged it leaks out and the levels become elevated in the blood.  ALT is specific to the liver, so it is a good indicator of liver damage, but it is only useful in dogs, cats, rabbits and primates.  Large animals have very little ALT so SDH and GLDH are used instead.

Increased ALT can be caused by:
-Artifact: In cats hemolysis can result in elevated ALT levels when no liver damage is present.
-Drugs: Anti-seizure medication such as primidone, phenobarbitone, dilantin will increase ALT levels up to four times normal. Corticosteroids increase ALT up to 2-3 x normal. Any other drugs that cause hepatotoxicity may also raise ALT such as: tetracycline in cats, caparsolate in dogs, or acetaminophen.
-Liver disease: conditions that alter cell membrane permeability or cause necrosis will cause ALT levels to rise and ALT will usually be higher than AST in cases of liver disease.
-Bile duct obstruction: if bile backs up it will begin breaking down tissue which may lead to elevated ALT.
-Trauma: if liver cells are hurt or destroyed ALT levels may become elevated.
-Muscle disease: in severe cases such as ischemic myopathy in cats, muscular dystrophy in dogs ALT my become elevated but AST and CK levels will rise to a much greater degree.
-Cancer: hepatic neoplasia can also cause ALT levels to rise although in this case AST is usually higher than ALT.


Decreased ALT can be caused by:
There is no such thing as ALT levels that are "too low".