| Intended Use | : | Glucose-6-phosphate dehydrogenase (G6PD) is aninvolved in energy production. It is found in all cells, including red blood cells (RBCs) and helps protect them from certain toxic by-products of cellular metabolism. A deficiency in G6PD causes RBCs to become more vulnerable to breaking apart () under certain conditions. This test measures the amount of G6PD in RBCs to help diagnose a deficiency. G6PD deficiency is a genetic disorder. When individuals who have inherited this condition are exposed to a trigger such as stress, an infection, certain drugs or other substance(s), significant changes occur in the structure of the outer layer (cell membrane) of their red blood cells. Hemoglobin, the life-sustaining, oxygen-transporting protein within RBCs, forms deposits (precipitates) called. Some individuals may experience these reactions when exposed to fava beans, a condition called "favism." With these changes, RBCs can break apart more readily, causing a decrease in the number of RBCs. When the body cannot produce sufficient RBCs to replace those destroyed, hemolytic anemiaresults and the individual may developjaundice, weakness, fatigue, and/or shortness of breath. G6PD deficiency is the most common enzyme deficiency in the world, affecting more than 400 million people. It may be seen in up to 10% of African-American males and 20% of African males. It is also commonly found in people from the Mediterranean and Southeast Asia. G6PD deficiency is inherited, passed from parent to child, due to or changes in the G6PD that cause decreased enzyme activity. There are over 440 variants of G6PD deficiency. The G6PD gene is located on the sex-linked X. Since men have one X and one Y sex chromosome, their single X chromosome carries the G6PD gene. This may result in a G6PD deficiency if a male inherits the single X chromosome with an altered gene. Since women have two X sex chromosomes, they inherit two copies of the G6PD gene. Women with only one mutated gene () produce enough G6PD that they usually do not experience any symptoms (i.e.,asymptomatic), but under situations of stress, they may demonstrate a mild form of the deficiency. In addition, a mother may pass the single mutated gene to any male children. Rarely do women have two mutated gene copies (), which could result in G6PD deficiency. G6PD deficiency is a common cause of persistent jaundice in newborns. If left untreated, this can lead to significant brain damage and mental retardation. Most people with G6PD deficiency can lead fairly normal lives, but there is no specific treatment apart from prevention. They must be cautious and avoid certain medications such as aspirin, phenazopyridine and rasburicase, antibiotics with "sulf" in the name and dapsone, anti-malarial drugs with "quine" in the name, foods such as fava beans, and chemical substances such as naphthalene (found in moth balls). Note that fava beans, often called broad beans, are commonly grown in the Mediterranean area. Acuteviralandbacterialinfections can also initiate episodes of hemolytic anemia as well as elevated levels of acid in the blood (i.e.,acidosis). Individuals should consult with their healthcare practitioner to get a comprehensive list of these triggers. A good starting point is the list found on theG6PD Deficiency Favism Association website. With hemolytic anemia, RBCs are destroyed at an accelerated rate and the person affected becomes pale and fatigued (anemic) as their capacity for providing oxygen to their body decreases. In severe cases of RBC destruction, jaundice can also be present. 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 person may require a blood transfusion. This condition can be fatal if not treated. A small percentage of those affected with G6PD deficiency may experienceanemia. |
| Frequently Asked Questions (FAQs) | : | Q: Why get tested? A: To determine whether you have an inherited G6PD deficiency Q: When toi get tested? A:When you have had one or more intermittent bouts ofhemolytic anemiathat may be triggered by an infection or certain medications Q: How it is used? A: When a child experienced persistent jaundice as a newborn for unknown reasons; A:Glucose-6-phosphate dehydrogenase (G6PD) enzyme testing is used to screen for and help diagnose G6PD deficiencies. It may be used to screen children who had unexplained persistentjaundiceas a newborn. Currently, newborns are not routinely screened for G6PD deficiency; however, this is dependent upon the specific state that provides the testing. According to the National Newborn Screening and Genetics Resource Center, as of November 2014, two states provide G6PD testing as part of their newborn screening panel: Pennsylvania and the District of Columbia. G6PD is anenzymefound in all cells, including red blood cells (RBCs), and helps protect them from certain toxic by-products of cellular metabolism. A deficiency in G6PD causes RBCs to become more vulnerable to breaking apart (hemolysis) under certain conditions. (For more on this, see the"What is being tested?"section.) G6PD testing may also be used to help establish a diagnosis for people of any age who have had unexplained episodes ofhemolytic anemia, jaundice, or dark urine. If the person had a recentorillness or was exposed to a known trigger (such as fava beans, a "sulfa" drug, or naphthalene), followed by a hemolytic episode, then G6PD deficiency may be considered. Repeat G6PD testing may occasionally be ordered to confirm initial findings. Screening tests typically involve a simplequalitativetest that only tells if the person has a certain high level of G6PD in his or her cells. Confirmation testing will involve aquantitativetest, with which the actual amount of enzyme activity is measured. In the most common form of G6PD deficiency seen in persons of African ancestry, G6PD levels are normal in newly produced cells but decrease up to 75% as the RBCs age. Because of this, testing is not recommended until several weeks after a hemolytic episode resolves. During the episode, a higher percentage of the older, more fragile G6PD-deficient RBCs are typically destroyed, leaving the newer, less deficient cells to be tested, potentially masking a G6PD deficiency. Genetic testing is not routinely done but can be ordered as follow up to an enzyme test(s) that indicates a deficiency to determine which G6PDare present. At this time, more than 440 G6PD gene variations have been identified and can cause deficiencies of varying severity depending on the mutation(s) and on the individual person. Some mutations do not change the G6PD enzyme activity. The World Health Organization has classified the G6PD mutations into five groups based on the enzyme levels and their impact on the affected person’s health. However, only the most common G6PD mutations are identified during testing. If a specific mutation is known to be present in a family line, tests to detect that particular mutation can also be conducted. Several facilities that offer this unique testing are provided on the siteGenetic Testing Registry. Q: When it is ordeered? A:G6PD enzyme testing is primarily performed when an individual hasandassociated withhemolytic anemia. Testing may be done when someone has had an episode of increased RBC destruction but after the crisis has resolved. Some signs and symptoms include: - Fatigue, weakness
- Pale skin ()
- Fainting
- Shortness of breath
- A rapid heart rate
- Jaundice
- Red or brown urine (from the presence of blood/hemoglobin)
- Enlarged spleen
Testing may also be done when other laboratory test results are consistent with a hemolytic anemia. These may show increasedbilirubinconcentrations (bulirubinemia), hemoglobin in the urine (hemoglobinuria), decreasedRBC countandhaptoglobin levels, increasedreticulocyte countandlactate dehydrogenase levels, presence ofon ablood smear, and sometimes the presence ofinside the RBCs on a specially stained blood smear. G6PD activity testing is typically ordered when other causes ofanemiaand jaundice have been ruled out and several weeks after an incident has been resolved. If available, screening may be performed on a newborn in the first day or two after birth. Q: Why is the detection of G6PD deficiency is important? A: The detection allows people to work with their healthcare practitioner and to educate themselves about a condition that will affect them to some degree for their entire lives. It also allows people to talk to the healthcare practitioner about how this trait is inherited and the potential impact it may have on their children. By knowing about the deficiency and avoiding potential triggering substances and situations, most of those who have G6PD deficiencies can lead relatively normal lives. |
