At a Glance
Why Get Tested?
To screen for or monitor treatment for a liver or bone disorder
When to Get Tested?
As part of a routine liver panel or when you have symptoms of a liver or bone disorder
A blood sample drawn from a vein in your arm
Test Preparation Needed?
Fasting overnight preferred but not required
The Test Sample
What is being tested?
Alkaline phosphatase (ALP) is an enzyme found in several tissues throughout the body, including liver, bone, kidney, bowel (intestine), and in the placenta of women who are pregnant. The highest concentrations of ALP are present in the cells that comprise bone and the liver. This test measures the level of ALP in the blood.
In the liver, ALP is found on the edges of cells that join to form bile ducts, tiny tubes that drain bile from the liver to the bowels, where it is needed to help digest fat in the diet. ALP in bone is produced by special cells called osteoblasts that are involved in the formation of bone. Each of the various tissue types produces distinct forms of ALP called isoenzymes.
Elevated levels of ALP in the blood are most commonly caused by liver disease or bone disorders. Levels of the enzyme can be greatly increased, for example, in cases where one or more bile ducts are blocked. Smaller increases of blood ALP are seen in liver cancer and cirrhosis, with use of drugs toxic to the liver, and in hepatitis. Any condition causing excessive bone formation, including bone disorders such as Paget's disease, can cause increased ALP levels. Children and adolescents typically have higher blood ALP levels because their bones are still growing. As a result, the ALP test must be interpreted with different reference (normal) values for children and for adults.
It is possible to distinguish between the different forms (isoenzymes) of ALP produced by different types of tissues in the body. If it is not apparent from clinical signs and symptoms whether the source of a high ALP test result is from liver or bone disease, then a test may be performed to determine which isoenzyme is increased in the blood.
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Fasting is preferred but not required for this test. Eating a meal can increase the ALP level slightly for a few hours in some people. It is usually better to do the test after fasting overnight. In this case, only water is permitted.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
ALP Isoenzyme Test. (Update May 5, 2013.) National Center for Biotechnology Information PubMed Health. Available online at http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0003968 through http://www.ncbi.nlm.nih.gov/pubmedhealth. Accessed September 2013.
Alkaline Phosphatase, Total and Isoenzymes, Serum. Mayo Clinic. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/89503 through http://www.mayomedicallaboratories.com. Accessed September 2013.
ALP – Blood Test. (Updated May 30, 2011). MedlinePlus. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003470.htm. Accessed September 2013.
Xiushui, M. R. et. al. (Updated March 2, 2012.) Cardiac Cirrhosis and Congestive Hepatopathy. Medscape. Available online at http://emedicine.medscape.com/article/151792 through http://emedicine.medscape.com. Accessed September 2013.
Sources Used in Previous Reviews
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby; 1998.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006 Pp 608-609, 624.
Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006, Pp 49-51.
Carey, W (January 1, 2009) Approach to the Patient with Liver Disease: A Guide to Commonly Used Liver Tests, Cleveland Clinic. Available online at http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/hepatology/guide-to-common-liver-tests/ through http://www.clevelandclinicmeded.com. Accessed October 2009.
Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson RA and Pincus MR, eds. Philadelphia: 2007, Pp 86, 256.
(2000) Dufour, DR et al. National Academy of Clinical Biochemistry Standards of Laboratory Practice: Laboratory Guidelines for Screening, Diagnosis and Monitoring of Hepatic Injury. Available online at http://www.aacc.org/SiteCollectionDocuments/NACB/LMPG/hepatic/hepatic_combined.pdf#page=3 through http://www.aacc.org. Accessed October 2009.
Harrison's Principles of Internal Medicine. 16th ed. Kasper D, Braunwald E, Fauci A, Hauser S, Longo D, Jameson JL, eds. McGraw-Hill, 2005, Pp 1815, 2280-2281.