Glucose 6-Phosphate Dehydrogenase (G6PD), Quantitative, Whole Blood and Red Blood Cell Count (RBC)

Whole blood

8 mL (4 mL in each of two tubes)

RBC: two 500-μL lavender-top Microtainer™ tubes filled to at least 50% of tube capacity (Note: If any other size lavender tube is used, the tube must be filled to at least 50% capacity of tube fill volume. Insufficient volume may limit the extent of procedures performed.); and G6PD: one lavender-top (EDTA) tube, green-top (heparin) tube or yellow-top (ACD) tube (0.1 mL) whole blood (Note: This volume does not allow for repeat testing.)

Two lavender-top (EDTA) tubes; or one green-top (heparin) tube and one lavender-top (EDTA) tube; or one yellow-top (ACD) tube and one lavender-top (EDTA) tube

This test is used to evaluate glucose 6-phosphate dehydrogenase (G6PD) deficiency. G6PD deficiency, an X-linked disorder, is the most common enzymatic disorder of red blood cells in humans, affecting more than 400 million people worldwide. The clinical expression of G6PD variants encompasses a spectrum of hemolytic syndromes. Affected patients are most often asymptomatic, but many patients have episodic anemia, while a few have chronic hemolysis.

With the most prevalent G6PD variants (G6PD A- and G6PD Mediterranean), hemolysis is induced in children and adults by the sudden destruction of older, more deficient erythrocytes after exposure to drugs having a high redox potential (including the antimalarial drug primaquine and certain sulfa drugs) or to fava beans, selected infections or metabolic abnormalities. In the neonate with G6PD deficiency, however, decreased bilirubin elimination may play an important role in the development of jaundice.

G6PD deficiency should be suspected in any subject with an episode of nonimmune hemolytic anemia, especially if occurring after drug ingestion, infection or an episode of diabetic ketoacidosis.

False normal results after hemolysis may occur; vide infra. See Additional Information.

Levels of G6PD are higher in the newborn than they are in the adult.

When high levels are seen in older patients, it invariably reflects the presence of a young red blood cell population with reticulocytosis.

Kinetic − 340 nm

See table.

G6PD hemolysis is associated with formation of Heinz bodies in peripheral red blood cells. It is the older erythrocytes that are most G6PD-deficient in affected individuals. These cells are first eliminated in a hemolytic crisis. The younger cells and reticulocytes contain more G6PD. For these reasons, after a hemolytic crisis, when only younger erythrocytes and reticulocytes are present, the G6PD values may be spuriously normal.

These "false-negative" (ie, spuriously normal or high) results are a potential concern because the most severely deficient red cells have already been removed from the circulation via hemolysis.

This problem is usually not important when testing male Caucasians but is a concern in some Caucasian females and blacks of both sexes, especially during the reticulocytosis following acute hemolysis. When a false-negative test is suspected, the best approach is to reëvaluate the patient three months after the hemolytic episode, a time at which the red cell mass will have been repopulated with red cells of all ages.

To prevent future hemolytic episodes, subjects with G6PD deficiency should avoid drugs and chemicals with oxidant potential. A partial list of safe and unsafe drugs is given in following table.