glucose-6-phosphate dehydrogenase [de-hy-DRAW-jen-aze] deficiency, G6PD deficiency, G6PDD
This is a blood test to determine whether you have low amounts of an enzyme called glucose-6-phosphate dehydrogenase. Experts estimate that 400 million people worldwide have a G6PD deficiency. This enzyme deficiency is a genetic disorder that affects mostly males. A mutation in the G6PD gene causes the red blood cells to break down prematurely. Early blood cell destruction is called hemolysis. Some people who have the defective gene never have any symptoms. Others have varying degrees of hemolytic anemia, which means that red blood cells are destroyed faster than new ones can be made.
Most of the time, if you have a moderate deficiency of glucose-6-phosphate dehydrogenase, you feel fine. But triggers can set off hemolysis. The effect is the sudden destruction of older, more deficient red blood cells. These triggers include:
Eating fava beans or inhaling pollen from a fava plant
Certain sulfa drugs
You might have this test if you have some of these symptoms:
Pale or yellow skin
Yellowing in the whites of the eyes
Rapid heart rate
Shortness of breath
A newborn with G6PD deficiency can be born with jaundice and might have this test if symptoms such as dark urine, pale stools, and increasing bilirubin levels continue after the second week of life.
If you have only a mild to moderate deficiency and you have an important reason to take a drug that will trigger hemolysis, your health care provider may offer you a low dose of the trigger drug and monitor your blood count closely. The monitoring test is called a complete blood count.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
Here are some general results:
A normal test result indicates G6PD activity in your blood cells. A normal – or no G6PDD – result for adults is 5.5 to 20.5 units/gram of hemoglobin.
Less than 10 percent of normal means that you have severe deficiency and chronic hemolytic anemia.
Others with severe enzyme deficiency may not have chronic hemolytic anemia but will have intermittent anemia.
Those with moderate deficiency, meaning 10 to 60 percent of normal ranges, may have intermittent hemolytic anemia that is usually associated with certain drugs or infection.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
If you take this blood test during, or just after, a hemolysis episode, the result could be falsely normal. The false-negative result could occur because most of the blood cells with greater G6PD deficiency (the older ones) have already been destroyed and the remaining blood cells are not, or not yet, G6PD-deficient. If your health care provider suspects a false-negative result, you will most likely have your blood checked again in about three months. At this point, you'll have had time to develop blood cells of various ages.
You don't need to prepare for this test. Be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.