AST ALT AP SDH GGT

Liver Enzymes

Indications for performing this test:  These enzymes are often included on a standard serum biochemistry profile, though the enzymes included for each species will vary from laboratory to laboratory.  Liver enzymes are not function tests, and their presence in the serum indicates possible liver pathology.  Liver enzymes are helpful in determining the extent of liver pathology that is taking place in an animal with suspected hepatic disease. 

Liver Enzyme Categories:

  • Enzymes released by hepatocellular death: 

These enzymes are  Aspartate Aminotransferase (AST),  Alanine Aminotransferase (ALT), and Sorbitol Dehydrogenase (SDH).  Elevations in these enzymes indicate hepatocellular damage, but do NOT indicate a cause. Hepatocytes can be damaged by any condition causing hypoxia whether by toxins, cholestasis, or the presence of inflammatory or neoplastic cells in the liver.  

 

  • Enzymes induced by cholestasis or drugs:   

These enzymes are Alkaline Phosphatase (AP) and Gamma Glutamyltransferase (GGT).  Drugs such as corticosteroids may induce the production of these enzymes.  Cholestatis or biliary obstruction is also known to induce the production of these enzymes.  

Consider this learning issue: There are 2 different types of liver enzymes  - one type is RELEASED from damaged hepatocytes while the other type is INDUCED (production increased) in response to cholestasis or drugs.  So ..... why do we so commonly see BOTH types of enzymes elevated?  And ... what sorts of conditions would be expected to result in an increase in just one type of liver enzymes - at least initially?        

Click on the links at the top of the page to read more about each individual liver enzyme.

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