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
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
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. Drugs that may affect the ALP level may include:
- Birth control pills
- Certain diabetes medicines
- Male hormones
- Narcotic pain medicines
- Nonsteroidal anti-inflammatory drugs (NSAIDs), used for arthritis and pain)
- Tricyclic antidepressants
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
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.
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.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
Higher-than-normal ALP levels may be due to:
- Biliary obstruction
- Bone disease
- Eating a fatty meal if you have blood type O or B
- Healing fracture
- Liver disease
- Osteoblastic bone tumors
- Paget’s disease
Lower-than-normal ALP levels (hypophosphatasemia) may be due to:
- Protein deficiency
- Wilson’s disease
Additional conditions under which the test may be performed:
- Alcoholic liver disease (hepatitis/cirrhosis)
- Biliary stricture
- Giant cell (temporal, cranial) arteritis
- Multiple endocrine neoplasia (MEN) II
- Renal cell carcinoma
What the risks are
Berk PD, Korenblat KM. Approach to the patient with jaundice or abnormal liver test results. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 150.
Pratt DS. Liver chemistry and function tests. In: Feldman M, Friedman LS, Brandt LJ, eds. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease. 9th ed. Philadelphia, Pa: Saunders Elsevier; 2010:chap 73.