Alkaline phosphatase (ALP) is a protein found in all body tissues. Tissues with higher amounts of ALP include the liver, bile ducts, and bone.
A blood test can be done to measure the level of ALP.
A related test is the ALP isoenzyme 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 6 hours before the test, unless your health care provider tells you otherwise.
Many medicines can interfere with blood test results.
- Your 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
This test may be done:
- To diagnose liver or bone disease
- To check if treatments for those diseases are working
- To check for side effects from medicines
The normal range is 44 to 147 international units per liter (IU/L) or 0.73 to 2.45 microkatal per liter (µkat/L).
Normal values may vary slightly from laboratory to laboratory. They also can vary with age and sex. 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
Abnormal results may be due to the following conditions:
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 of bone
Lower-than-normal ALP levels
- Pernicious anemia
- Protein deficiency
- Wilson disease
- Zinc deficiency
Other conditions for which the test may be done:
Fogel EL, Sherman S. Diseases of the gallbladder and bile ducts. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 146.
Korenblat KM, Berk PD. Approach to the patient with jaundice or abnormal liver tests. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 138.
Martin P. Approach to the patient with liver disease. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 137.
Pincus MR, Abraham NZ, Bluth M. Interpreting laboratory results. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 9.
Review Date 5/1/2021
Updated 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, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.