Alkaline phosphatase (ALP) is an enzyme found in many body tissues such as liver, bile ducts, bone, and intestine. There are several different forms of ALP called isoenzymes. The structure of the enzyme depends on where in the body it is produced. This test is most often used to test ALP made in the tissues of the liver and bones.
The ALP isoenzyme test is a lab test that measures the amounts of different types of ALP in the blood.
It may also be done to check liver function and to see how medicines you take may affect your liver.
The normal value is 20 to 140 IU/L (international units per liter).
Adults have lower levels of ALP than children. Bones that are still growing produce higher levels of ALP. During some growth spurts, levels can be as high as 500 IU/L. For this reason, the test is usually not done in children, and abnormal results refer to adults.
The isoenzyme test results can reveal whether the increase is in "bone" ALP or "liver" ALP.
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The example above shows the common measurement range for results for these tests. Some laboratories use different measurements or may test different specimens.
Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.