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.
The alkaline phosphatase test is a related test.
How the Test is Performed
A blood sample is needed. Most of the time blood is drawn from a vein located on the inside of the elbow or the back of the hand.
How to Prepare for the Test
You should not eat or drink anything for 10 to 12 hours before the test, unless your health care provider tells you to do so.
Many medicines can interfere with blood test results.
- Your health care provider will tell you if you need to stop taking any medicines before you have this test.
- DO NOT stop or change your medicines without talking to your provider first.
How the Test will Feel
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Why the Test is Performed
When the alkaline phosphatase (ALP) test result is high, you may need to have the ALP isoenzyme test. This test will help determine what part of the body is causing higher ALP levels.
This test may be used to diagnose or monitor:
- Bone disease
- Liver, gallbladder, or bile duct disease
- Pain in the abdomen
- Parathyroid gland disease
- Vitamin D deficiency
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.
What Abnormal Results Mean
Higher-than-normal ALP levels:
- Biliary obstruction
- Bone disease
- Eating a fatty meal if you have blood type O or B
- Healing fracture
- Liver disease
- Osteoblastic bone tumors
- Paget disease
Lower-than-normal levels of ALP:
Levels that are only slightly higher than normal may not be a problem unless there are other signs of a disease or medical problem.
Alkaline phosphatase isoenzyme test
Berk P, Korenblat K. Approach to the patient with jaundice or abnormal liver tests. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 147.
Fogel EL, Sherman S. Diseases of the gall bladder and bile ducts In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 155.
Martin P. Approach to the patient with liver disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 146.
Weinstein RS. Osteomalacia and rickets. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 244.
Update Date 5/3/2015
Updated by: 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.