Alkaline phosphatase (ALP) is a protein found in all body tissues. Tissues with particularly high amounts of ALP include the liver, bile ducts, and bone.
A blood test can be done to measure the level of ALP.
See also: ALP isoenzyme test
Why the Test is Performed
This test is done to diagnose liver or bone disease, or to see if treatments for those diseases are working. It may be included as part of a routine liver function test.
How the Test is Performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around your upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.
Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
How to Prepare for the Test
You should not to eat or drink anything for 6 hours before the test, unless otherwise instructed by your doctor.
Many drugs affect the level of alkaline phosphatase in the blood. Your health care provider may tell you to stop taking certain drugs before the test. Never stop taking any medicine without first talking to your doctor.
- Anti-inflammatory medicines
- Birth control pills
- Certain arthritis drugs
- Certain diabetes medicines
- Male hormones
- Narcotic pain medicines
- Tricyclic antidepressants
The normal range is 44 to 147 IU/L (international units per liter).
Normal values may vary slightly from laboratory to laboratory. They also can vary with age and gender. High levels of ALP are normally seen in children undergoing growth spurts and in pregnant women.
What Abnormal Results Mean
Higher-than-normal ALP levels may be due to:
- Biliary obstruction
- Bone disease
- Healing fracture
- Liver disease
- Osteoblastic bone cancers
- Paget's disease
Lower-than-normal ALP levels (hypophosphatasemia) may be due to:
- Protein deficiency
Additional conditions under which the test may be performed:
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.