What is a G6PD test?
A G6PD test measures the levels of glucose-6-phosphate dehydrogenase (G6PD), an enzyme in your blood. An enzyme is a type of protein that’s important for cell function.
G6PD helps red blood cells (RBCs) function normally. It also protects them from potentially harmful byproducts that can accumulate when your body is fighting infection or as the result of certain medications. A lack of G6PD may make RBCs more vulnerable to breaking down in a process called hemolysis.
A G6PD test is a simple test that requires a blood sample. It’s typically ordered to test for G6PD deficiencies.
A G6PD deficiency is an inherited disorder. It’s most common in men of African, Asian, or Mediterranean descent. It’s the result of X-linked recessive transmission, which means it’s much more likely to affect men as opposed to women. The deficiency can lead to a certain type of anemia known as hemolytic anemia. The G6PD test is often used to determine the causes of hemolytic anemia.
G6PD protects oxygen-rich RBCs from chemicals called reactive oxygen species (ROS). ROS build up in your body:
- during a fever or infection
- when you take certain medications
- when you eat fava beans
If your G6PD levels are too low, your RBCs won’t be protected from these chemicals. The blood cells will die, leading to anemia.
Certain foods, medications, infections, and severe stress can trigger a hemolytic episode. A hemolytic episode is the rapid destruction of RBCs. In people with hemolytic anemia, the body can’t produce enough RBCs to replace those that have been destroyed.
Your doctor may order a G6PD test if they suspect you have hemolytic anemia based on symptoms such as:
- an enlarged spleen
- fainting
- fatigue
- jaundice
- pale skin
- rapid heart rate
- red or brown urine
- shortness of breath
A G6PD test is most often ordered after a doctor has ruled out other causes of anemia and jaundice. They’ll perform the test once a hemolytic episode has subsided.
Your doctor may also order the test to monitor treatments or confirm the findings of other blood tests.
Blood draws are routine procedures that rarely cause serious side effects. In very rare cases, the risks of giving a blood sample can include:
- hematoma, or bleeding under your skin
- excessive bleeding
- fainting
- infection at the site of needle puncture
Some medications can interfere with these test results. Tell your doctor which medications you’re taking, including prescriptions and nutritional supplements. They may advise you to stop taking them before your G6PD test. Testing shouldn’t be performed soon after a blood transfusion. This may invalidate the results.
Let your doctor know if you’ve recently eaten fava beans or taken sulfa drugs. Sulfa drugs may include:
- antibacterial or antifungal drugs
- diuretics, or water pills
- anticonvulsants
Sulfa drugs can produce adverse reactions, especially in people with G6PD deficiencies.
Your G6PD test may be delayed if you’re experiencing a hemolytic episode. Many cells with low levels of G6PD are destroyed during an episode. As a result, your test results may show falsely normal G6PD levels.
Your doctor will give you complete instructions on how to prepare for your blood draw. It won’t be necessary to fast, or not eat or drink, before a G6PD test.
The blood draw may be performed in a hospital or specialized testing facility.
A nurse or technician will clean the site before the test to prevent any microorganisms on your skin from contaminating it. Then they’ll wrap a cuff or other pressure device around your arm. This will help your veins become more visible.
The technician will draw several samples of blood from your arm. They’ll place gauze and a bandage over the puncture site once the test is completed. Your blood samples will be sent to a laboratory for testing. Results will be forwarded to your doctor when they’re complete.
According to Mayo Medical Laboratories, normal levels for people 1 year and older are 8.8-13.4 units per gram of hemoglobin (U/gHb).
Your doctor will discuss the results from your G6PD test at a follow-up appointment.
Low levels of G6PD in your blood indicate an inherited deficiency. There’s no cure for this disorder. However, you can prevent hemolytic episodes and anemic symptoms by avoiding certain triggers.
Triggers related to a G6PD deficiency hemolytic episode include:
- eating fava beans
- sulfa drugs
- naphthalene, a compound found in moth repellent and toilet bowl deodorizers
Other potential triggers include taking aspirin (Bayer) and other nonsteroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen (Advil).
There are other substances that your doctor will know to avoid, as they may cause complications. These substances include:
- methylene blue
- nitrofurantoin (Macrobid, Macrodantin), a drug used to treat urinary tract infections (UTIs)
- phenacetin, a pain medication
- primaquine, an antimalarial drug
- quercetin, a prominent ingredient in some dietary supplements
