Alkaline Phosphatase

Why this test may be ordered

• As part of a routine checkup
• To screen for or help diagnose liver diseases
• To screen for or help diagnose bone disorders
• If you have symptoms of liver damage
• If you have symptoms of a bone disorder

Preparation and collection

Your provider will let you know if there are any special instructions. An ALP test is usually ordered with other blood tests. You usually need to fast (not eat or drink) for several hours before these tests. You may need to stop taking certain medicines before the test, so tell your provider about everything you take. But don't stop taking any medicines unless your provider tells you to.

During the test, a health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. This usually takes less than five minutes.

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

Understanding results

High alkaline phosphatase (ALP) levels may be a sign of a liver problem or a bone disorder. But your ALP test results can't tell which type of ALP is high.

• What does high alkaline phosphatase mean?

  High ALP - possibly from the liver: High alkaline phosphatase levels from your liver may be a sign of: blockages in your bile ducts, cirrhosis, hepatitis, mononucleosis, which can sometimes cause swelling in the liver. Limitation: It's possible to have higher than normal levels of ALP and not have a medical condition that needs treatment. Next step: If your test results show high ALP levels, your provider may order other tests to help figure out what's causing the problem.
• High ALP with normal liver tests - possibly from bone: If alkaline phosphatase levels are high and the results of liver tests are normal, the problem may be a bone disorder, such as Paget's disease of bone. Limitation: Children and teens may have high levels of ALP because their bones are growing. Next step: Your provider will consider your symptoms, medical history, and other test results to make a diagnosis.
• Low ALP: Low levels of ALP are less common. They may be a sign of: zinc deficiency, protein deficiency, malnutrition, pernicious anemia, thyroid disease, Wilson disease, hypophosphatasia, a rare genetic disease that affects bones and teeth. Limitation: Birth control pills and certain medicines may lower ALP levels, while other medicines can cause the levels to increase. Next step: To learn what your results mean, talk with your provider.

• The test alone cannot identify the source of elevated ALP (liver vs. bone).
• Higher than normal levels may not indicate a medical condition needing treatment.
• Many factors such as pregnancy, age, medications, and recent meals can affect ALP levels.
• An ALP isoenzyme test to differentiate sources may not be available everywhere.
• Low levels are less common and may require further evaluation.

What to do next

To learn what your results mean, talk with your provider.

• What does an alkaline phosphatase test measure?
• Why would my provider order this test?
• Do I need to fast before the test?
• What do high or low results mean?
• What other tests might be needed?

Evidence source

Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.

U.S. National Library of Medicine: Alkaline Phosphatase

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