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 eat or drink anything for 10 to 12 hours before the test, unless your doctor tells you to do so.

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. The following drugs may affect the level of alkaline phosphatase in the blood:

• Allopurinol
• Antibiotics
• Anti-inflammatory medicines
• Birth control pills
• Certain diabetes medicines
• Chlorpromazine
• Cortisone
• Male hormones
• Methyldopa
• Narcotic pain medicines
• Nonsteroidal anti-inflammatory drugs (NSAIDs, used for arthritis and pain)
• Propranolol
• Tranquilizers
• 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

When the alkaline phosphatase (ALP) test result is high, the doctor may order 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:

• Bone disease
• Cause of pain in the abdomen
• Liver, gallbladder, or bile duct disease
• 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.

Normal Results

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 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:

• Bone diseases or problems, such as healing fractures, certain bone tumors, softening of the bones,hyperparathyroidism, orPaget's disease
• Gallstones, or a blockage in the tubes that carry bile from the liver
• Liver disease or infection of the liver (hepatitis)
• Lymphoma or leukemia

Lower-than-normal levels of ALP:

• Malnutrition
• Protein deficiency
• Wilson's disease

Levels that are only slightly higher than normal may not be a problem unless there are other signs of a disease or medical problem.

Risks

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Alternative Names

Alkaline phosphatase isoenzyme test

References

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.

Update Date: 4/1/2012

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.