Alkaline Phosphatase (ALP)

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.

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