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.
How the test is performed
A sample of your blood will be taken out of a vein.
The chemical NBT is added to the white blood cells in the lab. The cells are then examined under a microscope to see id the chemical has made them turn blue.
How to prepare for the test
If a child is having the test, it may be helpful to explain what will happen and how the test will feel. Knowing the "how and why" may help the child relax.
How the test will feel
There may be slight pain or stinging feeling when the needle is inserted to draw blood. There may be some throbbing at the site after the blood is taken.
Why the test is performed
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 from one lab to another. Talk to your doctor about the meaning of your test results.
What abnormal results mean
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.
What the risks are
There is very little risk involved with having blood taken. Veins and arteries vary in size so taking blood may be harder in some people than in others.
Other slight risks from having blood drawn may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.