What Is the G6PD Test?

Medically Reviewed by Sabrina Felson, MD on May 29, 2023
Written by WebMD Editorial Contributors
4 min read

G6PD is an enzyme called glucose-6-phosphate dehydrogenase. It is a type of housekeeping protein that has many different activities in the body.

G6PD is responsible for protecting your cells from chemical and environmental damage, also known as oxidative damage.

Reactive oxygen species are also called free radicals. They are unstable molecules that easily react with other molecules. Your body normally makes these as part of its activities, but too many can be harmful. The G6PD enzyme makes chemicals that stop these from building up in your blood. 

If free radicals build up, they can damage your cells. Red blood cells are especially sensitive to free radicals.

A lack of G6PD causes your red blood cells to break down faster than they are made, which is called hemolysis. When your body can’t make up for the quick loss, you can get hemolytic anemia. ‌

Hemolytic anemia can be dangerous because it causes a loss of oxygen to your organs and tissues. 

The G6PD test is a blood test that measures how much of this enzyme you have in your blood. If you have low amounts, you have a condition called G6PD deficiency. 

G6PD deficiency is a hereditary condition caused by a mutation, or a change, in your G6PD gene. This gene tells your body to make the G6PD enzyme, so a mutation will lower the amount of this useful protein in your body.

Not everyone who has G6PD deficiency has other health problems. The deficiency alone is not enough to cause anemia or problems with your red blood cells. However, individuals who already have this mutation can have new symptoms triggered by outside sources. 

These triggers raise the amount of reactive oxygen species in your body. When you have an increase in compounds and not enough G6PD to clear them, you can get sick. These triggers include:

Fava beans have certain chemicals that quickly turn to free radicals. People who have G6PD deficiency can have a reaction to fava beans that causes sudden onset hemolytic anemia. This is called favism.

Men are more likely than women to have G6PD deficiency. It’s more common in some areas like Africa, Asia, and the Mediterranean. In the United States, African-American men are most commonly affected.

Your doctor might order the G6PD test if you have these symptoms:

  • Severe tiredness
  • Pale skin
  • Shortness of breath
  • Fast heartbeat
  • Yellow skin 
  • Yellow eyes
  • Dark urine
  • Enlarged spleen
  • Back pain
  • Belly pain
  • Weakness
  • Confusion

If your baby is born with jaundice, or yellow skin and eyes, they might have G6PD deficiency. It’s common for babies to have jaundice in the first few days of life. If it lasts past 2 weeks and they have dark urine, pale stools, and high bilirubin levels, your doctor might test for G6PD deficiency. 

Test results are different for everyone. They might also be different depending on the lab as some labs use different measurements than others. There are some general results, though.‌

Normal. A normal test result means you have enough of the enzyme and don’t have G6PD deficiency. A normal measurement is 5.5 to 20.5 units/gram of hemoglobin for adults.

Moderate deficiency. A moderate deficiency means the amount of G6PD enzyme in your blood is at 10% to 60% of the normal range. Someone with a moderate deficiency might have hemolytic anemia that comes and goes. It is usually linked to your medications or an infection.

Severe deficiency. A severe deficiency means you have less than 10% of the normal range of G6PD enzymes in your blood. If you have a severe deficiency, you might have ongoing hemolytic anemia. Sometimes people with severe deficiency have anemia that comes and goes. 

Most people with G6PD are asymptomatic, and most people who have symptoms only have them when they are under increased oxidative stress from medication or infection. You can manage the condition by avoiding triggers. This will stop you from developing hemolytic anemia.

You will want to:

  • Avoid aspirin and acetaminophen
  • Avoid fava beans
  • Avoid certain antibiotics
  • Avoid malaria medication
  • Treat infections right away

Most people who have hemolysis don’t have any symptoms. If you have mild symptoms, your doctor might suggest folic acid and iron pills. If the hemolysis leads to anemia, you might need a blood transfusion and oxygen therapy.

While antioxidants do fight free radicals, they may not be helpful to this condition. Antioxidants like vitamin E don’t help G6PD deficiency. 

If you have G6PD deficiency, make sure to talk to your doctor about your medical history and any symptoms you’re having.