Leukocyte alkaline phosphatase is a test that tells how much of a protein called alkaline phosphatase (ALP) you have inside your white blood cells. Leukocyte means white blood cell.

See also: Alkaline phosphatase (ALP) test

Blood is typically 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 the 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.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

A laboratory specialist separates the white blood cells from the rest of the blood sample and watches to see if any substances stick to specific colored dyes. Substances that contain phosphate, such as ALP, attach to certain colored dyes.

You should not eat or drink for 6 hours before the test.

Certain medicines can affect the test results. Your health care provider may tell you to stop taking such medications. These medications include:

• Allopurinol
• Androgens
• Anti-inflammatory medicines
• Birth control pills
• Certain antibiotics
• Certain arthritis drugs
• Certain diabetes drugs (taken by mouth)
• Chlorpromazine
• Cortisone
• Methyldopa
• Narcotics
• Propranolol
• Tranquilizers
• Tricyclic antidepressants

NEVER stop taking any medicine without first talking to your doctor.

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.

ALP is found in different forms throughout the body. This test is done to confirm a number of different medical conditions, including certain types of anemia and leukemia.

Your doctor may also order this test if you have an increase in platelet levels in the blood.

A staining score of 20 to 100 (out of a maximum of 400) is considered normal.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Higher-than-normal results may be due to:

• Essential thrombocytosis
• Leukemoid reaction
• Myelofibrosis
• Polycythemia vera

Lower-than-normal results may be due to:

• Aplastic anemia
• Chronic granulocytic leukemia
• Pernicious anemia

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but 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)

Hoffman R, Benz Jr. EJ, Shattil SJ, et al., eds. Hematology: Basic Principles and Practice. 4th ed. Philadelphia, Pa: Churchill Livingston; 2005:803-804.

Goldman L, Ausiello D. Cecil Textbook of Medicine. 22nd ed. Philadelphia, Pa: WB Saunders; 2004:987-988.