What is being tested?This test measures the activity of glucose-6-phosphate dehydrogenase (G6PD) in the blood. G6PD is an enzyme that helps produce energy from glucose and helps protect cells, especially red blood cells (RBCs), from the effects of oxidation. If there is insufficient G6PD activity inside RBCs, they 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 the hemoglobin (oxygen-carrying protein) inside them and breaking the RBCs apart.
G6PD deficiency is the most common enzyme deficiency in the world, affecting about 400 million people, according to the Nemours Foundation. Mutations or changes in the G6PD gene may lead to the production of a G6PD enzyme that has diminished function or stability. This is expressed as decreased enzyme activity levels.
So far, more than 350 G6PD gene variations have been identified, but only a few of them are common. They cause enzyme activity deficiencies of varying severity, depending on the mutation and on the individual patient. Since the G6PD gene is located on the X chromosome, of which males only have one, males will have a G6PD deficiency if their G6PD gene is affected. Females have two X chromosomes and two G6PD genes. Heterozygous females (those with one altered gene) produce both G6PD deficient and non-deficient RBCs. They frequently do not experience any symptoms and may not be identified unless 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 experience G6PD deficiency.
In newborns, G6PD deficiency may cause persistent jaundice - yellow skin and eyes due to the build up of bilirubin. Left untreated, this jaundice can lead to organ damage and mental retardation. Once it is resolved, however, the newborn jaundice does not usually return.
Most people with G6PD deficiency can lead fairly normal lives, but they must be cautious to avoid certain medications, foods (such as fava beans), chemical substances (such as naphthalene, found in moth balls), and infections (bacterial and viral) that can cause oxidative stresses and lead to bouts of hemolytic anemia. With hemolytic anemia, RBCs are destroyed at an accelerated rate and the patient may become pale and fatigued as their capability of providing oxygen to their body decreases. Most of these episodes are self-limiting, but some of the RBCs may be destroyed faster than the body can replace them, and the affected patient may require a blood transfusion. A small percentage of those affected with G6PD may experience chronic anemia.
