What is ALT (Liver Enzyme)?
An enzyme measured in blood tests to evaluate liver health; elevated levels usually indicate damage to liver cells.
ALT (alanine aminotransferase) is an enzyme concentrated mainly inside liver cells. When these cells are damaged — by inflammation, infection, toxin exposure, or injury — the enzyme leaks into the bloodstream, and its levels rise on a blood test. Because of this, ALT is one of the main markers used to evaluate liver health in dogs and cats.
Elevated ALT levels can indicate anything from mild, temporary causes, such as a reaction to medication or an inappropriate diet, to more serious conditions, such as hepatitis, toxin exposure (for example, from certain plants, medications, or chemicals), liver tumors, or metabolic diseases that secondarily affect the organ, such as diabetes. Elevated ALT alone does not indicate the cause — it only signals some degree of injury to liver cells, which is why it is usually evaluated together with other enzymes and imaging studies.
The test is done through a blood draw, usually as part of a broader chemistry panel. It is important to remember that animals can have elevated ALT without showing any visible symptoms, which reinforces the importance of routine testing, especially in middle-aged and senior pets or before anesthetic procedures. Any abnormal result should always be interpreted by a veterinarian, who will consider the pet's complete clinical picture.
Important notice
This calculator is for educational purposes and does not replace a veterinary evaluation. When in doubt, consult a veterinarian.Related terms
Complete Blood Count (CBC)
A blood test that evaluates red blood cells, white blood cells, and platelets, used to investigate anemia, infection, inflammation, and clotting problems.
Creatinine
A waste product removed by the kidneys, measured in blood to evaluate kidney function; elevated levels usually indicate that the kidneys are not filtering properly.
BUN (Blood Urea Nitrogen)
A substance produced by the liver from the breakdown of protein and eliminated by the kidneys; measured together with creatinine to evaluate kidney function.