G6PD Deficiency in Black Adults: Triggers, Symptoms, Testing

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme defect in the world, and it is common in people of African ancestry: roughly 1 in 10 Black American men carry the African A- variant. The enzyme normally protects red blood cells from oxidative stress. When it runs low, certain drugs, infections, fava beans, and even mothball fumes can make red cells rupture, a process called hemolysis, which causes a sudden anemia. Most people with the A- variant feel completely healthy until a trigger hits.

G6PD is an enzyme inside every red blood cell. It powers the pathway that makes NADPH, the molecule that neutralizes oxidative damage. Without enough G6PD, red cells cannot defend themselves against oxidative stress, so they break apart when a trigger raises that stress. An estimated 400 million people worldwide have G6PD deficiency, making it the most common enzyme deficiency on the planet.

The reason it concentrates in people of African, Mediterranean, Middle Eastern, and South Asian descent is malaria. The same low enzyme activity that puts red cells at risk also makes them a worse host for the malaria parasite, so the trait spread in regions where Plasmodium falciparum malaria was endemic. The African A- variant is the version most Black Americans carry. It is classed as a milder form: it does not usually cause ongoing anemia, but it leaves red cells vulnerable to sudden breakdown when an oxidant trigger appears.

The gene sits on the X chromosome, so the condition is X-linked. Men have one X, so a single altered copy makes them deficient, which is why prevalence in Black men runs around 10 percent. Women have two X chromosomes and usually need both copies altered for a full deficiency, though carriers can still have lower enzyme levels and occasional symptoms because of random X-inactivation. This is a separate gene from sickle cell. The two conditions are both common in Black families and can travel together, but one does not cause the other. If you carry sickle cell trait, you can read more in our guide on sickle cell trait and family planning.

The single most useful thing a person with G6PD deficiency can do is know the trigger list and carry it to every appointment. Oxidant drugs are the clearest danger because a clinician can prescribe one without knowing your status. The strongest-evidence drug triggers include:

• Rasburicase (used for high uric acid in cancer care), which is contraindicated in G6PD deficiency.
• Dapsone, a potent oxidant used for some infections and skin conditions.
• Primaquine and tafenoquine, antimalarials that require G6PD testing before use.
• Some sulfa antibiotics such as sulfamethoxazole, plus nitrofurantoin (a common urinary tract infection drug).
• Phenazopyridine (the bladder-pain pill that turns urine orange), methylene blue, and nalidixic acid.

Beyond drugs, three everyday triggers matter. Fava beans (broad beans) can set off a severe episode called favism, typically 24 to 72 hours after eating them. Naphthalene mothballs, and clothes or bedding stored with them, release fumes that trigger hemolysis, a real risk for infants in deficient households. And infection is actually the most common trigger of all: the oxidative stress your body mounts against bacteria and viruses, including salmonella, E. coli, viral hepatitis, and influenza, can be enough to break red cells. Ask your clinician or pharmacist to check any new prescription against a G6PD-unsafe drug list before you fill it.

When red cells break down in large numbers, the signs come on over a day or two after exposure to a trigger. The classic picture is dark urine, the color of cola or strong tea, from hemoglobin spilling into it. Alongside that, people develop jaundice, a yellowing of the whites of the eyes and, on brown and Black skin, often most visible in the eyes, palms, and the roof of the mouth rather than the skin tone itself. Add fatigue and weakness from the dropping red-cell count, and back pain or belly pain as the breakdown products process through the kidneys and spleen. A racing heart and pale or grayish lips and nail beds signal that the anemia is getting severe.

In the A- variant, the episode is usually self-limited. The body destroys the oldest, most vulnerable red cells first, then makes new ones, and symptoms ease within a week once the trigger is removed. But a severe episode can drop the blood count fast enough to need a transfusion, and the dark urine can stress the kidneys, so it is not something to ride out at home without a plan. If your fatigue is more of a slow, chronic drain than a sudden crash, the cause may be something else entirely, such as the iron-deficiency anemia covered in our piece on anemia and iron deficiency.

G6PD deficiency is one of the leading causes of severe newborn jaundice worldwide, and it matters for Black families because the trait is common. A deficient newborn can build up bilirubin faster and tolerate it worse, raising the risk of kernicterus, a preventable form of bilirubin brain injury. G6PD deficiency has been reported in a meaningful share of kernicterus cases. The good news is that this is highly preventable: hospitals watch at-risk infants closely, and treatment with phototherapy, or an exchange transfusion in severe cases, stops the bilirubin from reaching dangerous levels. If G6PD deficiency runs in your family, tell the delivery team so your baby is monitored, and keep naphthalene mothballs out of the house entirely.

The test is a quantitative G6PD enzyme assay, a blood test that measures how much working enzyme your red cells have. It is the definitive test and is more reliable than the older fluorescent spot screen, which can miss female carriers. One timing rule is critical: do not rely on a test taken during or right after a hemolytic episode. The crisis destroys your oldest red cells, the ones with the least enzyme, leaving behind young red cells and reticulocytes that carry near-normal enzyme levels. That can make a deficient person test falsely normal. Wait until the episode has fully resolved, generally a few weeks to about three months, then test or retest.

If you are a Black man, knowing your status before you ever need a high-risk drug is worth asking for, especially before cancer treatment that might use rasburicase, before antimalarials for travel, or before starting dapsone. The result follows you for life, so it is a one-time test that protects every future prescription.

Management is mostly avoidance: know your trigger list, share it with every prescriber and pharmacist, treat infections promptly, and skip fava beans and mothballs. Ask your primary care clinician for a quantitative G6PD test if you have never been tested and either have a family history or have had an unexplained jaundice or dark-urine episode. A hematologist can confirm the diagnosis, document your safe and unsafe drug lists, and counsel your family, since the trait is inherited. To find a Black hematologist or a clinician who serves Black patients, search our provider directory. Carry a wallet card or phone note listing G6PD deficiency and the drugs to avoid, so any clinician treating you, even in an emergency, sees it.