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Nitroblue tetrazolium test
Alternative namesNBT test
DefinitionThis 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
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.
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 testIf 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 feelWhen 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 performedThis test is performed as a screen for CGD.
Normal ValuesNormally, 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 meanIf 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 areRisks associated with having blood drawn are slight:
Update Date: 9/3/2003Michael 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.
Last updated: Tue, 06 Jan 2009 00:20:03 GMT