Blood biochemistry: alkaline phosphatase (ALP)

Blood biochemistry: alkaline phosphatase (ALP)
(ALP, Serum alkaline phosphatase, SAP)

Overview

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).

Uses

Alone

Identification of cholestasis.

Screening for bone disease.

In combination

As part of routine biochemical screening panel.
Liver disease in conjunction with:
- Aspartate aminotransferase (AST) .
- Alanine aminotranferase (ALT) .
- Gamma-glutamyltransferase (GGT) .
- Bile salts .
Investigation of suspected hyperadrenocorticism .

Other points

High levels of ALP (and GGT) occur in canine colostrum.
May see <100x increase following colostral ingestion.
May take approximately 10 days to return to within reference interval for adult dogs.

Sampling

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Source of test material

Standard venipuncture .
For sample tube preference see .

Quantity of test material

2 ml serum or plasma. Check with laboratory regarding minimum recommended volume for single test or in combination with other tests.

Quality control

Precautions

Avoid hemolysis/lipemia.

Timing of test

Fast animal for 8-12 h before sampling to prevent sample lipemia.

Sample storage

Refrigerate prior to despatch.
Avoid excessive temperatures.

Sample transport

Standard postal times adequate
Package according mailing regulations
Separate serum/plasma prior to despatch

Test(s)

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Methodologies

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

Availability

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

Validity

Sensitivity

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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Normal (reference) values

US

Example of reference interval: 0-120 umol/l.
No absolute values - individual laboratories should supply normal range for their test.
<300 IU/L probably not pathological.

Abnormal values

Increased [ALP]

Cholestasis (up to 150 fold increase).
Liver damage (infectious hepatitis , toxic hepatitis , chronic active hepatitis , severe trauma, primary neoplasia , cirrhosis , acute pancreatitis ).
Steroid induced - SIAP (hyperadrenocorticism , glucocorticoid therapy).
Bone disease:
- Hyperparathyroidism .
- Panosteitis .
- Bone tumors .
- Bone healing.
- Craniomandibular osteopathy .
In general elevations in non-hepatic disease are much lower than in liver disease except for glucocorticoid induction which may result in very high ALP levels. Levels >1000 give strong suspicion of exposure to glucocorticoids..
ALP usually increases within 6 days after glucocorticoid administration, but may not reach peak for 3-4 weeks.
May require months for ALP to return to within reference interval following steroid withdrawal.

Errors and Artifacts

Increased in dogs <1 year old due to bone metabolism/growth.
Anticonvulsants, barbiturates and glucocorticoids induce ALP.
May also see induction with ketoconazole, phenylbutazone.

Sources

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Publications

Refereed papers

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.

Vetstream contributor(s)

Dr Kathleen P Freeman DVM MS PhD , Idexx Laboratories, PO Box 4, Wetherby, West Yorkshire LS22 4ZR, UK.

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	Blood biochemistry: alanine aminotransferase (SGPT ALT)
	Blood biochemistry: aspartate aminotransferase (AST)
	Blood biochemistry: bile acids
	Blood biochemistry: gamma glutamyltransferase
	Blood sample tube requirements table 01
	Bone: neoplasia
	Canine adenovirus type 1 disease
	Chronic hepatitis
	Craniomandibular osteopathy
	Hyperadrenocorticism
	Hyperparathyroidism (primary)
	Jugular venipuncture
	Liver: chronic disease
	Liver: cirrhosis
	Liver: neoplasia
	Liver: toxic hepatitis
	Pancreatitis: acute
	Panosteitis
	Transportation of diagnostic specimen

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