G6PD deficiency: oxidant haemolysis, Heinz bodies and bite cells
- Lesion
Red cells cannot defend against oxidants. After certain drugs, infections or fava beans, haemoglobin clumps and cells burst a few days later.
What it is
Glucose-6-phosphate dehydrogenase (G6PD) supplies NADPH through the pentose phosphate pathway, keeping glutathione reduced so red cells can neutralize oxidants. The deficiency is X-linked and very common in malaria-endemic regions, because it protects against falciparum malaria. Most variants make a normal-functioning but unstable enzyme, so older red cells are the most deficient. Oxidant stress denatures haemoglobin into Heinz bodies, causing intravascular and extravascular haemolysis that is usually episodic and self-limited.
Structure
- Smear during a crisis: bite cells, blister cells, some spherocytes, reticulocytosis in recovery.
- Supravital (crystal violet) stain: Heinz bodies attached to the membrane.
Step by step
- An oxidant (from infection, drug or fava beans) generates hydrogen peroxide inside red cells.
- Low G6PD activity means too little NADPH to regenerate reduced glutathione.
- Haemoglobin sulfhydryl groups oxidize; globin denatures and precipitates as Heinz bodies.
- Heinz bodies damage the membrane: some cells lyse inside vessels.
- Splenic macrophages pluck out the inclusions, leaving bite cells, then remove the damaged cells.
- Older, enzyme-poor cells die first; reticulocytes with more enzyme survive and the episode ends.
Markers
- Heinz bodies
- Bite cells
- G6PD activity assay
Clinical notes
- Sudden pallor, jaundice, dark urine and back pain a few days after an infection or drug.
- Screening matters before primaquine for vivax malaria, which is common in Colombia.
- Measuring G6PD during a crisis can be falsely normal because young cells have more enzyme.
Test yourself
Think of the answer, then tap the question to see it.
Why does haemolysis in G6PD A− deficiency stop even if the drug is continued?
Older cells with the least enzyme are destroyed first; the young cells that replace them have enough activity to resist.
What are Heinz bodies?
Precipitates of oxidized, denatured haemoglobin attached to the red cell membrane, seen with supravital stains.
Why is G6PD deficiency common in some populations?
It protects heterozygotes against severe falciparum malaria.
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Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: G6PD gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.