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

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore blood flow. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants and young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

A laboratory specialist seperates the white blood cells from the rest of the blood sample and watches to see if any substances attach to certain colored dyes. Substances that contain phospate, 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.

Higher-than-normal results may be due to:

• Leukemoid (leukemia-like) reaction
• Myelofibrosis
• Polycythemia vera

Lower-than-normal results may be due to:

• Aplastic anemia
• Chronic granulocytic leukemia
• Pernicious anemia

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

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.

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.