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Ency. home > Test > G > Glucose-6-phosphate dehydrogenase

Glucose-6-phosphate dehydrogenase   

Overview | Risks | Results

Alternative names:

RBC G6PD test; G6PD screen

Definition:

The RBC G6PD test measures the amount (activity) of the enzyme G6PD in red blood cells.

How the Test is Performed

Adult or child:
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and a tourniquet (an elastic band) or blood pressure cuff is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the tourniquet to distend (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 tourniquet is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

Infant or young child:
The area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

How to Prepare for the Test

Adult:
No special preparation is usually necessary.

Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the Test is Performed

This test is performed when the diagnosis of G6PD deficiency is suspected.

Red blood cells are almost solely dependent on blood glucose as a source of energy. This biochemical pathway is called glycolysis. Red blood cells can also divert glucose into a secondary pathway which results in the production of NADPH from NADP.

NADPH plays an important role in maintaining the proper 3-dimensional structure of proteins in the cell membranes and also in maintaining hemoglobin in the reduced state. Oxidized hemoglobin (i.e., met-hemoglobin) is unable to bind oxygen. The secondary pathway requires the enzyme G6PD.

A deficiency of G6PD results in hemolysis (destruction) of red blood cells. There are many kinds of G6PD deficiency, and in most cases an additional environmental factor is necessary to bring about a hemolytic episode.

Hemolytic episodes can be triggered by drugs (e.g., sulfonamides, nitrofurantoin, phenacetin, antipyretics, primaquine, quinidine, thiazide diuretics, and tolbutamide), infections, severe stress, or certain foods (such as, fava beans).

It is important that this test not be performed in the setting of an acute hemolytic episode. Following hemolysis, the cells most likely to have low G6PD levels (older cells) have been destroyed, and those remaining may show normal G6PD levels. 

Following recovery from the episode, aged cells will show the decreased levels of G6PD, resulting in a positive test.

Ency. home > Test > G > Glucose-6-phosphate dehydrogenase

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