Glucose-6-Phosphate Dehydrogenase

Why is the Test 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 (nicotinamide adenine dinucleotide phosphate).

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 biochemical pathway needed for the generation of NADPH 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 (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.