Glucose-6-phosphate dehydrogenase
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.
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)
- Nitrofurantoin
- Phenacetin
- Primaquine
- Sulfonamides
- Thiazide diuretics
- Tolbutamide
- Quinidine
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 Results
What Abnormal Results Mean
Abnormal results mean you have a G6PD deficiency, which can cause hemolytic anemia in certain conditions.
Risks
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:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Alternative Names
RBC G6PD test; G6PD screen
References
Schwartz RS. Autoimmune and intravascular hemolytic anemias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 164.
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.
Update Date: 2/8/2012
Updated by: 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.
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