Also Known As
ALP
Alk Phos
Alkp
Alkaline phosphatase isoenzymes
Bone specific ALP
Formal Name
Alkaline Phosphatase
This article was last reviewed on
This article waslast modified on July 1, 2018.
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

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

Fasting overnight preferred but not required

You may be able to find your test results on your laboratory's website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab's website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab's website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called "normal" values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are "within normal limits."

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Alkaline phosphatase (ALP) is an enzyme found in several tissues throughout the body. The highest concentrations of ALP are present in the cells that comprise bone and the liver. Elevated levels of ALP in the blood are most commonly caused by liver disease or bone disorders. 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.

ALP blood levels can be greatly increased, for example, in cases where one or more bile ducts are blocked. This can occur as a result of inflammation of the gallbladder (cholecystitis) or gallstones. 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 drawn by needle from a vein in the arm.

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.

Accordion Title
Common Questions
  • How is it used?

    The alkaline phosphatase test (ALP) is used to help detect liver disease or bone disorders.

    • In conditions affecting the liver, damaged liver cells release increased amounts of ALP into the blood. This test is often used to detect blocked bile ducts because ALP is especially high in the edges of cells that join to form bile ducts. If one or more of them are obstructed, for example by a tumor, then blood levels of ALP will often be high.
    • Any condition that affects bone growth or causes increased activity of bone cells can affect ALP levels in the blood. An ALP test may be used, for example, to detect cancers that have spread to the bones or to help diagnose Paget's disease, a condition that causes malformed bones. This test may also sometimes be used to monitor treatment of Paget's disease or other bone conditions, such as vitamin D deficiency.

    If ALP results are increased but it is not clear whether this is due to liver or bone disease, tests for ALP isoenzyme may be done to determine the cause. A GGT test and/or a test for 5'-nucleotidase may also be done to differentiate between liver and bone disease. GGT and 5'-nucleotidase levels are increased in liver disease but not in bone disorders.

  • When is it ordered?

    An ALP test may be ordered as part of routine laboratory testing, often with a group of other tests called a liver panel. It is also usually ordered along with several other tests when a person has symptoms of a liver or bone disorder.

    Signs and symptoms of liver involvement may include:

    • Weakness, fatigue
    • Loss of appetite
    • Nausea, vomiting
    • Abdominal swelling and/or pain
    • Jaundice
    • Dark urine, light-colored stool
    • Itching (pruritus)

    Some examples of the signs and symptoms suggesting a bone disorder include:

    • Bone and/or joint pain
    • Increased frequency of fractures
    • Deformed bones
  • What does the test result mean?

    High ALP usually means that either the liver has been damaged or a condition causing increased bone cell activity is present.

    If other liver tests such as bilirubin, aspartate aminotransferase (AST), or alanine aminotransferase (ALT) are also high, usually the increased ALP is coming from the liver. If GGT or 5'-nucleotidase is also increased, then the high ALP is likely due to liver disease. If either of these two tests is normal, then the high ALP is likely due to a bone condition. Likewise, if calcium and/or phosphorus measurements are abnormal, usually the ALP is coming from bone.

    If it is not clear from signs and symptoms or from other routine tests whether the high ALP is from liver or bone, then a test for ALP isoenzymes may be necessary to distinguish between bone and liver ALP.

    ALP in liver disease
    ALP results are usually evaluated along with other tests for liver disease. In some forms of liver disease, such as hepatitis, ALP is usually much less elevated than AST and ALT. When the bile ducts are blocked (usually by gallstones, scars from previous gallstones or surgery, or by cancers), ALP and bilirubin may be increased much more than AST or ALT. ALP may also be increased in liver cancer.

    ALP in bone disease
    In some bone diseases, such as Paget's disease, where bones become enlarged and deformed, or in certain cancers that spread to bone, ALP may be increased.

    If a person is being successfully treated for Paget's disease, then ALP levels will decrease or return to normal over time. If someone with bone or liver cancer responds to treatment, ALP levels should decrease.

    Moderately elevated ALP may result from other conditions, such as Hodgkin's lymphoma, congestive heart failure, ulcerative colitis, and certain bacterial infections.

    Low levels of ALP may be seen temporarily after blood transfusions or heart bypass surgery. A deficiency in zinc may cause decreased levels. A rare genetic disorder of bone metabolism called hypophosphatasia can cause severe, protracted low levels of ALP. Malnutrition or protein deficiency as well as Wilson disease could also be possible causes for lowered ALP.

  • Is there anything else I should know?

    Pregnancy can increase ALP levels. Temporary elevations are also seen with healing fractures.

    Children and adolescents normally have higher ALP levels than adults because their bones are growing, and ALP is often very high during a growth spurt, which occurs at different ages in boys and girls.

    Some drugs may affect ALP levels. For example, oral contraceptives may decrease levels while anti-epileptics may increase levels.

  • What other tests are used to evaluate liver disorders?

    There are other commonly used liver tests that measure other enzymes found in liver cells, such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST). A test for bilirubin, a substance produced by the breakdown of red blood cells and removed from the body by the liver, may also be performed. Sometimes these tests (along with albumin and total protein testing) are run together as a liver panel. Other tests that may be performed individually or as part of a liver panel to detect or monitor liver disease include gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH), and prothrombin time (PT).

  • Who is at risk for liver disease and/or damage?

    Some of those who are at risk of liver disease include the following:

    See the article on Liver Disease for more on these.

  • What other laboratory tests may be done if I have a bone disorder?

    Depending on the cause, your condition may be diagnosed and/or monitored using other tests such as calcium, phosphorus, parathyroid hormone, vitamin D, or bone markers (a group of tests used to measure bone formation and bone resorption).

View Sources

Sources Used in Current Review

(2007) Golub, E. and Boesze-Battaglia, K. Current Opinions in Orthopaedics. Available online at http://josorge.com/publications/Citations/Bio-bio/004.pdf. Accessed July 13, 2016.

(Sept 2015) Mayo Clinic. Liver Function Tests. Available online at http://www.mayoclinic.org/tests-procedures/liver-function-tests/basics/why-its-done/prc-20012602. Accessed July 13, 2016.

(Apr 2015) MedlinePlus. ALP Blood Test. Available online at https://medlineplus.gov/ency/article/003470.htm. Accessed July 13, 2016.

(Mar 2015) Medscape. Biliary Obstruction Workup. Available online at http://emedicine.medscape.com/article/187001-workup. Accessed July 13, 2016.

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/. 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. 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.

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. Accessed September 2013.

Alkaline Phosphatase, Total and Isoenzymes, Serum. Mayo Clinic. Available online at http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/89503. 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. Accessed September 2013.

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