G6PD screen

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

Why the G6PD screen 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.

How the G6PD screen 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 G6PD screen

No special preparation is usually necessary.

How the G6PD screen 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.

Risks

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

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.

Normal Results

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.

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