The nitroblue tetrazolium test checks if certain immune system cells can change a colorless chemical called nitroblue tetrazolium (NBT) into a deep blue color.
A blood sample is needed.
The chemical NBT is added to the white blood cells in the lab. The cells are then examined under a microscope to see if the chemical has made them turn blue.
How to Prepare for the Test
No special preparation is needed.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
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.
The health care provider may order this test for people who have frequent infections in the bones, skin, joints, lungs, and other parts of the body.
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.
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person 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 lightheaded
- Multiple punctures to locate veins
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Glogauer M. Disorders of phagocyte function. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 169.
Riley RS. Laboratory evaluation of the cellular immune system. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 45.