ALT and ALP: different clues, not a liver score
Separate the information each enzyme provides, then connect it with symptoms, other findings and follow-up.
Prepared by TengRip · Guide updated：2026-10-25
Not veterinarian-reviewed; a report-reading guide, not a diagnosis.
Read these findings together
ALT mainly provides clues to liver-cell injury; ALP relates to cholestasis, bone and other influences. Do not add them together, cancel one against the other, or apply canine interpretation directly to cats.
This site does not list fixed normal values: reference ranges differ by analyzer and method, so always use the range printed on your report.
Work through your report
- Record each value, interval, date and previous result.
- List medicines and observed appetite, vomiting or color changes.
- Ask about complementary tests, imaging and follow-up.
| Test | Clues and limits | Related information |
|---|---|---|
| ALT | Mainly a clue to liver-cell injury, not a liver function score. | ALP, bilirubin, symptoms, and muscle or thyroid information when relevant. |
| ALP | Can relate to cholestasis, bone and other factors; feline and canine interpretation differs. | ALT, GGT, bilirubin and thyroid information when relevant. |
Alanine Aminotransferase (ALT)
An enzyme found mainly inside liver cells that leaks into the blood when those cells are injured. It is also often raised in hyperthyroid cats.
What it measures
ALT is an enzyme inside liver cells. When liver cells are injured and their membranes are damaged, ALT leaks into the blood. So it mainly shows whether liver cells are being injured, not how well the liver is working.
What a high value may mean
The main cause is liver cell injury, which has many possible reasons. In addition, some drugs can injure the liver (such as anticonvulsants and steroids); severe muscle damage can raise ALT, for example aortic thromboembolism in cats; and hemolysis in a cat's blood sample can cause a false increase. The American Animal Hospital Association (AAHA) guidelines also note that hyperthyroid cats often have raised ALT or ALP.
What a low value may mean
Interpretation focuses on high values; clinical interpretation guides do not list a low ALT as something that needs action.
Usually read together with
ALP, bilirubin, and other liver values; muscle enzymes if a muscle source is suspected. In senior cats, thyroxine (T4) as well.
When to follow up
How much ALT is raised and why needs your vet's overall judgment, and they may suggest a recheck, more liver tests, or imaging. If the cat also stops eating, vomits, or shows jaundice (yellow gums or whites of the eyes), see the vet promptly.
Section sources
Alkaline Phosphatase (ALP)
An enzyme linked to bile flow and bone activity. Cat livers contain little ALP and it lasts only about 6 hours in a cat's blood, so even mild increases in cats deserve attention.
What it measures
ALP is mainly used to check whether bile flow is blocked (cholestasis), and it also rises during bone growth or remodeling. Cats and dogs differ a lot here: cat liver cells contain little ALP, and liver ALP lasts only about 6 hours in a cat's blood (about 66 hours in dogs), so clinicians feel that small ALP increases in cats should not be ignored.
What a high value may mean
Possible causes include cholestasis (liver or bile duct disease); young, growing animals; some drugs (such as anticonvulsants); hyperthyroidism in cats (mainly the bone form of ALP); and bone healing or bone tumors. In dogs, steroid use and an overactive adrenal gland are also common causes; these are less common in cats.
What a low value may mean
Interpretation focuses on high values; clinical interpretation guides do not list a low ALP as something that needs action.
Usually read together with
ALT, GGT, bilirubin, and other liver values; in senior cats, thyroxine (T4).
When to follow up
A raised ALP in a cat is not always liver disease and may be hyperthyroidism, so your vet will need further tests to tell them apart. If your cat has had a poor appetite or has not eaten for several days and ALP is raised, see the vet promptly, because cats that go without food for a long time are at risk of fatty liver.
Section sources
Questions for the visit
- Which source or process is being investigated?
- Do other findings agree with the symptoms?
- What should be compared at follow-up?
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This site is for general reference only and is not a substitute for veterinary diagnosis. If your cat shows unusual signs, please see a vet promptly.