Alkaline Phosphatase
Reviewed
Also called: ALP, ALK, PHOS, Alkp, ALK PHOS
An alkaline phosphatase (ALP) test measures the amount of ALP in your blood. ALP is an enzyme found in all body tissues, with higher amounts in liver, bile ducts, and bones. Abnormal levels may indicate liver disease, bone disorders, or chronic kidney disease.
Specimen: Blood
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
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, but do not stop unless your provider tells you to.
A health care professional will take a blood sample from a vein in your arm, using a small needle. 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
Your ALP test results can't tell which type of ALP is high. Your provider will consider your symptoms, medical history, and other test results to make a diagnosis.
- High alkaline phosphatase (ALP) levels - possibly from liver: May indicate liver problems such as bile duct blockages, cirrhosis, hepatitis, or mononucleosis. Limitation: The test alone cannot determine the source of ALP; your provider will need additional tests. Next step: Your provider may order an ALP isoenzyme test or liver function tests.
- High alkaline phosphatase (ALP) levels - possibly from bone: May indicate a bone disorder such as Paget's disease of bone (abnormally large and weak bones). Limitation: The test alone cannot determine the source of ALP; your provider will need additional tests. Next step: Your provider may order an ALP isoenzyme test or other bone-specific tests.
- Low alkaline phosphatase (ALP) levels: May be a sign of zinc deficiency, protein deficiency, malnutrition, pernicious anemia, thyroid disease, Wilson disease, or hypophosphatasia (a rare genetic disease). Limitation: Low levels are less common and may require further evaluation. Next step: Your provider may order additional tests to determine the cause.
- 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
If results are abnormal, your provider may order additional tests such as an ALP isoenzyme test, liver function tests, or other tests to identify the underlying cause. They will consider your symptoms, medical history, and other test results.
- 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?