At a Glance
Why Get Tested?
To determine whether you have an inherited G6PD deficiency
When to Get Tested?
When a child experienced persistent jaundice as a newborn that was not due to another identified cause; when you have had one or more intermittent bouts of hemolytic anemia that appear to be triggered by infection or drugs
A blood sample drawn from a vein in your arm, by fingerstick, or by heelstick (newborns)
Test Preparation Needed?
Generally, none; however, if symptoms are acute, it is advised that you wait to be tested until after the episode has resolved.
The Test Sample
What is being tested?
Glucose-6-phosphate dehydrogenase (G6PD) is an enzyme involved in energy production. It is found in all cells including red blood cells (RBCs) and helps protect them from certain by-products of cellular metabolism. A deficiency in G6PD causes RBCs to become more vulnerable to breaking apart (hemolysis) when exposed to certain substances. This test measures the amount of G6PD enzyme in RBCs to help diagnose a G6PD 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), changes occur in the structure of the outer layer (cell membrane) of their red blood cells. Hemoglobin, the oxygen-transporting protein within RBCs, forms deposits (precipitates) called Heinz Bodies. 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 RBCs. When the body cannot produce sufficient RBCs to replace those that have been destroyed, then hemolytic anemia results and the individual may develop jaundice, weakness, fatigue, and/or shortness of breath.
G6PD deficiency 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 10% of African-American males in the U.S. and 20% of the male population in Africa. Depending on the specific location, it may occur in as low as 3% or more than 35% of the male population in the Mediterranean area and Southeast Asia.
G6PD deficiency is inherited, passed from parent to child. Inherited mutations or changes in the G6PD gene lead to decreased enzyme activity. There are over 440 variants of G6PD deficiency. The G6PD gene is located on the sex-linked X chromosome. 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.
Women have two X sex chromosomes; they thus inherit two copies of the G6PD gene. Women with only one altered gene (heterozygous) produce enough normal G6PD that they usually do not experience any symptoms, but under situations of stress they may demonstrate a mild form of the deficiency. In addition, the mother may pass the single altered gene to any male children. Rarely, a woman may have two altered gene copies (homozygous) and will experience G6PD deficiency.
G6PD deficiency is a common cause of persistent jaundice in newborns. Persistent jaundice, if left untreated, can lead to brain damage and mental retardation.
Most people with G6PD deficiency can lead fairly normal lives but must be cautious and avoid certain medications such as aspirin, antibiotics with "sulf" in the name, the anti-malarial drug quinine, foods such as fava beans, and chemical substances such as naphthalene (found in moth balls). Infections can also initiate episodes of hemolytic anemia.
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 red cell destruction, 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 person may require a blood transfusion. A small percentage of those affected with G6PD deficiency may experience chronic anemia.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm, by fingerstick, or by heelstick (newborns).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Generally, no test preparation is needed. However, if the individual is experiencing an episode in which symptoms of hemolytic anemia are acute, it is advised to postpone testing until the crisis has passed.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
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(© 1995-2012). Test ID: G6PD8368 Glucose-6-Phosphate Dehydrogenase (G-6-PD), Quantitative, Erythrocytes. Mayo Clinic May Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/8368 through http://www.mayomedicallaboratories.com. Accessed June 2012.
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(Updated 11 December 19). National Newborn Screening Status Report. National Newborn Screening and Genetics Resource Center [On-line information]. Available online at http://genes-r-us.uthscsa.edu/nbsdisorders.htm through http://genes-r-us.uthscsa.edu. Accessed June 2012.
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Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO. Pp 449-450.
(© 2004). Glucose-6-Phosphate Dehydrogenase. ARUP's Guide to Clinical Laboratory Testing [On-line information]. Available online at http://www.aruplab.com/guides/clt/tests/clt_a266.jsp#1149592 through http://www.aruplab.com.
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Matsui, W. (2007 February 26, Updated). Glucose-6-phosphate dehydrogenase deficiency. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000528.htm. Accessed on 8-27-08.
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(2006 May, Reviewed). Glucose-6-phosphate dehydrogenase deficiency. Genetics Home Reference [On-line information]. Available online at http://ghr.nlm.nih.gov/condition=glucose6phosphatedehydrogenasedeficiency through http://ghr.nlm.nih.gov. Accessed on 8-27-08.
(2006 September). What is Hemolytic Anemia. NHLBI [On-line information]. Available online at http://www.nhlbi.nih.gov/health/dci/Diseases/ha/ha_whatis.html through http://www.nhlbi.nih.gov. Accessed on 8-27-08.
G6PD Deficiency Favism Association, What is G6PD Deficiency? Available online at http://www.g6pd.org/favism/english/index.mv?pgid=intro through http://www.g6pd.org. Accessed September 2008.