Canis ISSN: 2398-2942

Blood biochemistry: alkaline phosphatase (ALP)

Synonym(s): ALP, Serum alkaline phosphatase, SAP

Contributor(s): Kathleen P Freeman


  • Membrane associated enzyme.
  • Number of isoenzymes produced in a range of tissues (liver, kidney, intestine, placenta).
  • Special procedures are necessary to determine isoenzymes.
  • Levamisole inhibition or heat activation commonly used to separate hepatic from steroidal isoenzymes as cause of increased activity.
  • May see overlap in steroid and hepatic isoenzymes in many types of disease so not always helpful in separating underlying cause.
  • Increased plasma levels are derived from liver and bone.
  • Good indicator of liver disease and cholestasis - increases before plasma bilirubin.
  • Corticosteroids induce a specific isoenzyme from the liver (steroid-induced alkaline phosphatase - SIAP/sALP).


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  • Method and normal range may vary between laboratories.
  • Electrophoretic or other separation method necessary to measure activity of individual isoenzymes, especially SIAP.


  • Widely available.
  • Routine test - contact laboratory to confirm availability of SIAP measurement.



  • Sensitive indicator of cholestasis or hyperadrenocorticism, but not specific.

Technique (intrinsic) limitations

  • Test results most significant when interpreted in conjunction with other laboratory results and clinical findings.

Result Data

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Further Reading


Refereed papers

  • Recent references from VetMedResource and PubMed.
  • Center S A, Slater M R, ManWarren T et al (1992) Diagnostic efficacy of serum alkaline phosphatase and gamma-glutamyltransferase in dogs with histologically confirmed hepatobiliary disease - 277 cases (1980-1990). JAVMA 201, 1258.

Other sources of information

  • Ettinger S J & Feldman E C (eds) (2000) Textbook of Veterinary Internal Medicine. 5th edn. Philadelphia: W B Saunders & Co.
  • Kaneko J J, Harvey J W & Brass M L (eds) (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Boston: Academic Press.
  • Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa: Iowa University Press.