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Definition:

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.



Alternative Names:

RBC G6PD test; G6PD screen



How the test is performed:

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.



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 Values:

Normal results are 8 - 8.6 units/gram of hemoglobin.

Normal value ranges may vary slightly among different laboratories. 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:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)


References:

Scwartz RS. Autoimmune and intravascular hemolytic anemias. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 164.




Review Date: 11/23/2008
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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Wentworth-Douglass Hospital
789 Central Avenue, Dover, NH 03820
Phone: (603) 742-5252
Toll free: 1 (877) 201-7100