Measuring liver enzymes is a common way for veterinarians to monitor the functioning of the liver. Increased, or elevated, liver enzymes in dogs usually indicates some type of liver disease. Even with higher than normal enzyme levels, however, a dog's liver may still function normally, making diagnosis tricky. Specific tests are needed on sick dogs to begin properly diagnosing what issues may be affecting the organ.
Testing for Increased Liver Enzymes
Testing for increased liver enzymes is a relatively easy blood draw. What is a little more complicated is choosing which enzymes to test and then interpreting those results in context. Four main enzymes are customarily checked in dogs suspected of having liver disease, according to the website Vetinfo. The status of several enzymes are evaluated simultaneously because one enzyme test may very well return with normal results, even if there is a problem, while there's a good chance not all will return with normal results if liver disease is present.
ALT and AST
Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) are two liver enzymes usually tested in conjunction with one another. ALT only occurs in the liver and increases when cells in the organ are damaged. Generally, the amount of increase in ALT is proportionate to the amount of liver damage. AST is an enzyme present not only in the liver, but in the heart and brain as well. However, an increase in ALT usually means an increase in AST if liver disease is present. If both enzymes are not elevated, the dog's health problems may be a result of something other than a problem with the liver.
ALP and GGT
Neither Alkaline Phosphate (ALP), nor Gamma Glutamyltransferase (GGT) are liver-specific enzymes. However, they are used in testing for liver disease because they are still good indicators of liver problems when used in conjunction with other tests. ALP levels are sensitive during the first stages of liver disease and will generally rise. GGTs are present in the kidneys and pancreas; in conjunction with other tests, a rise in GGTs can indicate liver disease.
Indicators of Liver Conditions
Illnesses commonly indicated by increased liver enzymes include liver cancer, Cushing's disease, and hepatitis.
Indicators of Other Diseases
Increased liver enzymes may be indicators of conditions besides liver problems. For instance, an increase in ALTs can mean heart failure or anaemia. An increase in ALPs may occur naturally in younger dogs, or be a result of anti-convulsive medications. An increase in GGTs by themselves is usually an indicator of kidney disease. Because elevated liver enzyme levels can point to a variety of problems, testing enzymes in conjunction with each other is important.