Glucose-6-phosphate dehydrogenase (G6PD) is a type of protein, called an enzyme, that helps red blood cells work properly. The G6PD test looks at the amount (activity) of this substance in a patient's red blood cells.
RBC G6PD test; G6PD screen
How the test is performed
A blood sample is needed. For information on how this is done, see: Venipuncture
How to prepare for the test
No special preparation is usually necessary.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Your doctor may order this test if you have signs of G6PD deficiency. This means you do not have enough G6PD activity.
Too little G6PD activity leads to the destruction of red blood cells. This process is called hemolysis. When this process is actively occurring, it is called a hemolytic episode.
Hemolytic episodes can be triggered by infections, severe stress, certain foods (such as fava beans), and certain drugs, including:
Antipyretics (drugs used to reduce fever)
If this test is done during a hemolytic episode it may be falsely positive and misleading. This is because the cells most likely to have low G6PD levels (older cells) have been destroyed, and those remaining may show normal G6PD levels.
After recovery from the episode, older cells will show lower levels of G6PD, resulting in a positive test.
Normal values vary and depend upon the laboratory used. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What abnormal results mean
Abnormal results mean you have a G6PD deficiency, which can cause hemolytic anemia in certain conditions.
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Yee DL, Bollard CM, Geaghan SM. Appendix: normal blood values: selected reference values for neonatal, pediatric, and adult populations. In: Hoffman R, Benz EJ, Shattil SS, et al, eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 164.
Todd Gersten, MD, Hematology/Oncology, Palm Beach Cancer Institute, West Palm Beach, FL. Review provided by VeriMed Healthcare Network. Also reviewed by Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington; David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.