MedlinePlus Medical Encyclopedia: Nitroblue tetrazolium test

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Nitroblue tetrazolium test

Contents of this page:
Illustrations Alternative names Definition How the test is performed How to prepare for the test	How the test will feel Why the test is performed Normal Values What abnormal results mean What the risks are

Illustrations

Nitroblue tetrazolium test

Alternative names Return to top

NBT test

Definition Return to top

This is a test that measures the ability of certain cells in the immune system to convert a colorless chemical, nitroblue tetrazolium (NBT), to a deep blue color.

How the test is performed Return to top

Blood is drawn from a vein, usually on 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 to apply pressure and restrict blood flow through the vein. 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 tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In the laboratory, NBT is added to a sample of white blood cells. The neutrophils (a type of white blood cell in your immune system that kill bacteria by ingesting them) normally make a chemical that kills the bacteria. In chronic granulomatous disease (CGD), this chemical is absent. As a result, neutrophils are able to ingest bacteria, but not kill them.

The chemical that kills the bacteria is the same that turns NBT from clear to deep blue. If the chemical is absent when NBT is added to the sample, it will not change color. This can be seen by looking at the white blood cells under an ordinary microscope.

How to prepare for the test Return to top

If your child is to have this test performed it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose for the procedure, the less anxiety they will feel.

How the test will feel Return to top

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 Return to top

This test is performed as a screen for CGD.

Normal Values Return to top

Normally, the sample and the neutrophils within it turn blue when NBT is added. This indicates that the neutrophils are producing the chemical necessary to kill bacteria.

What abnormal results mean Return to top

If the sample does not change color when NBT is added, the neutrophils are missing the chemical necessary to kill bacteria. This may indicate CGD.

What the risks are Return to top

Risks associated with having blood drawn are slight:

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

Update Date: 9/3/2003

Updated by: Michael C. Milone, M.D., Ph.D., Department of Pathology and Laboratory Medicine, University of Pennsylvania Medical Center, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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