What is being tested?This test measures the amount of glucose-6-phosphate dehydrogenase (G6PD) in the red blood cells (RBCs). G6PD is an
enzyme that protects red blood cells from the effects of oxidation. If there is insufficient G6PD, the RBCs become more vulnerable to
oxidative damage. If these RBCs are exposed to an oxidative agent (for a list,
click here), it changes their cellular structure, precipitating hemoglobin inside the cells (
Heinz Bodies), causing them to break apart (
hemolysis).
G6PD deficiency (most severe form is called Favism) is the most common enzyme deficiency in the world, affecting about 400 million people, according to the Nemours Foundation. It may be seen in up to 20% of the population in Africa, 4-30% in the Mediterranean, and in Southeast Asians. Mutations or changes in the G6PD gene may lead to the production of a G6PD enzyme that has diminished functionality or stability. This is expressed as decreased enzyme activity levels.
So far, more than 440 G6PD gene variations have been identified and can cause enzyme activity deficiencies of varying severity depending on the mutation and on the individual person. The G6PD gene is located on the X chromosome. Since males have one X and one Y chromosomes, the single X chromosome will carry the G6PD gene, thus resulting in a G6PD deficiency if the abnormal gene is inherited from the person’s mother. Females have two X chromosomes, thus two copies of the G6PD gene could possibly be inherited. Heterozygous females (those with only one altered gene) can produce enough normal G6PD that they usually do not experience any symptoms. However, the presence of the abnormal form may be identified if the deficiency is detected in their male children. Rarely, a female may be homozygous, having two altered G6PD genes (the same or different mutations), and thus will experience G6PD deficiency.
In newborns, G6PD deficiency may cause persistent jaundice. Left untreated, this jaundice can lead to brain damage and mental retardation.
Most people with G6PD deficiency can lead fairly normal lives, but they must be cautious to avoid certain medications (aspirin, sulfonamides, quinine), foods (such as fava beans), and chemical substances (such as naphthalene, found in moth balls), which can cause oxidative stress resulting in a hemolytic crisis. Infections, either bacterial or viral, can also cause oxidative stress and lead to bouts of hemolytic anemia. With hemolytic anemia, RBCs are destroyed at an accelerated rate and the patient becomes pale and fatigued (anemic) as their capacity for providing oxygen to their body decreases. In some cases, jaundice can also be present during episodes of hemolysis. Most of these episodes are self-limiting, but if a large number of RBCs are destroyed and the body cannot replace them fast enough, then the affected patient may require a blood transfusion. A small percentage of those affected with G6PD may experience chronic anemia.
