ALP Test
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 liver function tests or when a person has symptoms of a liver or bone disorder
Sample Required?
A blood sample taken from a vein in the arm
The Test Sample
What is being tested?
Alkaline phosphatase is an enzyme found in high levels in bone and liver. Smaller amounts of ALP are found in the placenta of women who are pregnant, and in the intestines. Each of these body parts makes different forms of ALP. The different forms are called isoenzymes.
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.
The Test
How is it used?
When a person has evidence of liver disease, very high ALP levels can tell the doctor that the person’s bile ducts are somehow partially or totally blocked or inflamed. Often, ALP is high in people who have cancer that has spread to the liver or the bones, and doctors can do further testing to see if this has happened. If a person with bone or liver cancer responds to treatment, ALP levels will decrease. When a person has high levels of ALP, and the doctor is unsure why, ALP isoenzyme tests might be requested to try to determine the cause.
When is it requested?
ALP is generally part of a routine laboratory test profile called liver function tests. It is usually requested with several other tests if a patient has symptoms of a liver or bone disorder.
What does the test result mean?
Raised levels of ALP are usually due to a disorder of either the bone or liver. If other liver function tests such as bilirubin, gamma-glutamyl transferase (GGT) or alanine aminotransferase (ALT) are also raised, this usually indicates that the ALP is coming from the liver. However if calcium and phosphate measurements are abnormal, this suggests that the ALP might be coming from bone. In some forms of liver disease, such as hepatitis, ALP is usually much less elevated than AST or ALT. However, when the bile ducts are blocked (for example by gallstones, scars from previous gallstones or surgery, or by a tumour), ALP and bilirubin may be increased much more than either AST or ALT. ALP can also be raised in bone diseases such as Paget’s disease (where bones become enlarged and deformed), or in certain cancers that spread to bone.
Is there anything else I should know?
Pregnancy can increase ALP levels. Children have higher ALP levels because their bones are growing, and ALP is often very high during the 'growth spurt' which occurs at different ages in males and females.
Eating a meal can increase the ALP level slightly for a few hours in some people. Ideally the test should be done after fasting overnight. Some drugs may increase ALP levels, especially some of the drugs used to treat psychiatric problems, but significant increases are rare.
Common Questions
Ask a Laboratory Scientist
Article Sources
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.
