The nitroblue tetrazolium test looks to see if certain immune system cells can change a colorless chemical called nitroblue tetrazolium (NBT) into a deep blue color.

NBT test

A blood sample is needed. For information on how this is done, see: Venipuncture

In the laboratory, the chemical NBT is added to a sample of white blood cells. The laboratory specialist looks at the cells under a microscope and determines if the NBT made them turn blue.

If your child is to have this test performed, it may be helpful to explain how the test will feel, and even demonstrate on a doll. Explain the reason for the test. Knowing the "how and why" may reduce the anxiety your child feels.

When the needle is inserted to draw blood, you may feel moderate pain or only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is done to screen for chronic granulomatous disease. This disorder is passed down in families. In people who have this disease, certain immune cells do not help protect the body from infections.

People who have frequent infections in the bones, skin, joints, lungs, and other parts of the body may have this test done.

Normally, the white blood cells turn blue when NBT is added. This means that the cells should be able to kill bacteria and protect the person from infections.

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

If the sample does not change color when NBT is added, the white blood cells are missing the substance needed to kill bacteria. This may be due to chronic granulomatous disease.

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)

Dinauer MC, Coates TD. Disorders of phagocyte function and number. In: Hoffman R, Benz EJ Jr, Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier;2008:chap 50.