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G6PD Deficiency
Roughly one in twenty people carry an inherited quirk in a single red-blood-cell enzyme, and most never know. The gene sits silent until a specific drug, a plate of raw fava beans, or a severe infection arrives. Then red cells break apart within a day or two: jaundice, dark urine, exhaustion, sometimes a hospital. That's G6PD deficiency, most common in people with African, Mediterranean, Middle Eastern, or Southeast Asian roots. The whole fix is one blood test and one line on your chart, for life.
Condition Evidence Strong Chapter Healthcare

Red blood cells have no backup. They can't repair themselves, and G6PD is the one enzyme that keeps them clear of the oxidative damage haemoglobin makes just by carrying oxygen 1. Lose enough of it and a strong trigger tips the cells over: haemoglobin oxidises, the cell stiffens, the spleen breaks it open. Enough cells at once over a day or two is a haemolytic crisis.

This is the most common enzyme defect in humans โ€” 400 to 500 million people carry a deficient variant 2. The map matches malaria almost exactly, because the variant protects against it: female carriers of the African form have about half the risk of severe malaria 3. About one in ten Black American men is deficient; across Mediterranean and Middle Eastern populations it runs 5% to 30% 4. The trade is protection from a historical killer for vulnerability to a few modern drugs and one bean.

The intervention is almost entirely paperwork. A blood test measures the enzyme; ask for the quantitative version that gives a percentage, because the old yes/no spot test misses affected women 5. In the US it usually costs tens of dollars.

Nothing about your body changes. You added a line to a record and a card to your wallet. What changes is a run of foreseeable moments years out. The next time you have a urinary infection, the pharmacist looks at the screen and picks a different antibiotic. The travel clinic swaps the antimalarial. The dentist catches the flag. Each is a non-event that would otherwise have been three days of haemolysis you didn't see coming. Multiply it across forty years of medical encounters: the crisis simply never happens, and no one around you ever hears the story.

The fine print โ€” when to skip it, and what people get wrong

The short, strong trigger list to avoid: primaquine, tafenoquine, dapsone, rasburicase, methylene blue, nitrofurantoin, phenazopyridine, plus raw or undercooked fava beans, naphthalene mothballs, and severe infections 7. Sulfa drugs are a grey zone โ€” flag any for your pharmacist. Longer lists exist, but risk there depends on dose and variant; a prescriber who knows your status can navigate them 8.

It's not a sulfa allergy. An allergy is an immune reaction in minutes; this is cell chemistry a day or two later 1. Women get it too: the gene is on the X chromosome, and a carrier can be as vulnerable as her brother. Eating fava beans once safely proves nothing; tolerance shifts day to day. Ancestry is a hint, not a screen: testing only high-risk newborns would miss about 44% of affected infants.

Almost every avoidable crisis is a documentation failure. A prescriber who didn't ask writes nitrofurantoin or Bactrim; two days later you're jaundiced โ€” the single most common scenario, and the one a problem-list entry prevents 5. A female carrier cleared by the old spot test crashes on a drug her brother was warned off 9. A newborn goes home on day two, before the day-four bilirubin peak 10.

References
  1. 1Luzzatto L, Ally M, Notaro R (2020). Glucose-6-phosphate dehydrogenase deficiency. Blood. link
  2. 2Nkhoma ET, Poole C, Vannappagari V, Hall SA, Beutler E (2009). The global prevalence of glucose-6-phosphate dehydrogenase deficiency: a systematic review and meta-analysis. Blood Cells, Molecules, and Diseases. link
  3. 3Uyoga S, Ndila CM, Macharia AW, et al. (2015). Glucose-6-phosphate dehydrogenase deficiency and the risk of malaria and other diseases in children in Kenya: a case-control and a cohort study. Lancet Haematology. link
  4. 4Howes RE, Piel FB, Patil AP, et al. (2012). G6PD deficiency prevalence and estimates of affected populations in malaria endemic countries: a geostatistical model-based map. PLoS Medicine. link
  5. 5Frank JE (2005). Diagnosis and management of G6PD deficiency. American Family Physician. link
  6. 6Cappellini MD, Fiorelli G (2008). Glucose-6-phosphate dehydrogenase deficiency. The Lancet. link
  7. 7Youngster I, Arcavi L, Schechmaster R, et al. (2010). Medications and glucose-6-phosphate dehydrogenase deficiency: an evidence-based review. Drug Safety. link
  8. 8FDA (2020). Elitek (rasburicase) prescribing information โ€” boxed warning: hemolysis and methemoglobinemia in G6PD-deficient patients. link
  9. 9Luzzatto L, Bancone G, Dugue PA, et al. (2023). New WHO classification of genetic variants causing G6PD deficiency. British Journal of Haematology. link
  10. 10Kemper AR, Newman TB, Slaughter JL, et al. (2022). Clinical Practice Guideline Revision: Management of Hyperbilirubinemia in the Newborn Infant 35 or More Weeks of Gestation. Pediatrics. link
Related in the handbook (6)
Related
  • โ€” G6PD deficiency is inherited; one test settles it for life and goes on your chart.
  • โ€” Another single-gene result that tells a doctor which drugs are dangerous for you.
  • โ€” When the wrong drug or fava beans hit, G6PD breaks red cells fast โ€” it's one of the hemolytic causes behind an unexplained anemia.
  • โ€” The whole intervention is one chart entry โ€” G6PD on your record so every doctor and pharmacist sees it.
  • โ€” G6PD is one of the genes that decides which drugs harm you โ€” exactly what a pharmacogenomic panel reads.
  • โ€” Nitrofurantoin, a go-to UTI antibiotic, can rupture red cells if you're G6PD-deficient โ€” flag the gene before you fill that script.
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