ALP (Alkaline phosphatase)

Alkaline phosphatase is an indicator of cholestasis in most species and osteoblastic activity in all species. In birds, it is primarily associated with osteoblastic activity, and is not useful for hepatobiliary diseases. Several isoenzymes are synthesised, but some have short half-lives and contribute little to serum ALP. Placental isoenzyme can be detected in late pregnancy in cats. Bone isoenzyme is associated with increased serum ALP in juvenile animals, bone remodelling and probably increased in feline hyperthyroidism. Hepatic isoenzyme has a short half-life in cats (6 hours), compared to dogs (70 hours), therefore the magnitude of ALP increase in feline liver disease is lower. In dogs, exogenous or endogenous corticosteroid hormones stimulate production of both the hepatic and glucocorticoid isoenzymes. The greatest increases in serum ALP are seen in cholestatic disorders and glucocorticoid excess, as well as some tumours. Phenobarbital induces ALP activity in the dog. In cats phenobarbitone and glucocorticoids have little effect, but hepatic lipidosis can be associated with marked ALP increases.  Major differentials for increased ALP include endocrine disease, cholestasis, neoplasia, age effects, and the effects of corticosteroid or anticonvulsant medication.


Dog, Cat, Avian. Not widely used in large animals


Plasma or Serum


Plain tube, gel or  heparin

Collection protocol:

Fasted sample preferred.


Reference(s): Center, S.A. Interpretation of Liver Enzymes. In: Veterinary Clinics of North America Small Animal Practice 37:2 March 2007  p 297 – 333. Stockham, S.L and Scott, M.A. Fundamentals of Veterinary Clinical Pathology 2nd Edition 2008. Thrall M.A. Veterinary Hematology and Clinical Chemistry 2006