Health Encyclopedia

Glucose-6-phosphate dehydrogenase

Definition

Glucose-6-phosphate dehydrogenase (G6PD) is a substance, called an enzyme, that helps red blood cells work properly. The G6PD test looks at the amount (activity) of this substance in red blood cells.

Alternative Names

RBC G6PD test; G6PD screen

How the test is performed

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore normal blood flow. Once the blood has been collected, the needle is removed. The puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleaned with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a small glass tube (pipette), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if bleeding continues.

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.

Too little G6PD 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
Nitrofurantoin
Phenacetin
Primaquine
Sulfonamides
Thiazide diuretics
Tolbutamide
Quinidine

You should not have this test during a hemolytic episode. 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 what your specific test results mean

What abnormal results mean

Abnormal results mean you have a G6PD deficiency, which can cause hemolytic anemia.

What the risks are

Excessive bleeding
Fainting or feeling light-headed
Blood collecting under the skin (hematoma)
Infection
Many needle sticks to find veins

Special considerations

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.

References

American Academy of Pediatrics Subcommittee on Hyperbilirubinemia. Management of Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation. Pediatrics. July 2004;114:297-316.

Wilmanski J, Villaneuva E, Deitch EA, Spolarics Z. Glucose-6-phosphate dehydrogenase deficiency and the inflammatory response to endotoxin and polymicrobial sepsis. Crit Care Med. February 2007;35:510-518.

Review Date:3/22/2007
Reviewed By:Carl T. Henningson Jr., MD, Private Practice specializing in Hematology and Oncology, Mansquan, NJ. Review provided by VeriMed Healthcare Network.

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