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Key Features

  • Hereditary enzyme defect causes episodic hemolytic anemia from decreased ability of red blood cells (RBCs) to deal with oxidative stresses

  • Leads to excess oxidized glutathione that forces hemoglobin to denature and form precipitants called Heinz bodies

  • Heinz bodies cause RBC membrane damage, which leads to premature removal of these RBCs by reticuloendothelial cells within the spleen (extravascular hemolysis)

  • 10–15% of American Blacks have the variant G6PD isoenzyme designated A–, in which there is both a reduction in normal enzyme activity and a reduction in stability and therefore no hemolytic anemia

  • A– isoenzyme activity declines rapidly as the RBC ages past 40 days, a fact that explains the clinical findings in this disorder

  • Mediterranean, Ashkenazi Jewish, and Asian variants have very low enzyme activity (class II G6PD activity)

  • Other classes of G6PD isoenzyme activity

    • Class I: low activity, with chronic, severe hemolysis

    • Class III: 10–60% activity with episodic hemolysis

    • Class IV: 60–150% activity (normal)

    • Class V: > 150% activity

  • Patients with G6PD deficiency seem to be protected from malaria parasitic infection, have less coronary artery disease, and possibly have fewer cancers and greater longevity

Clinical Findings

  • Usually healthy, without chronic hemolytic anemia or splenomegaly

  • Hemolysis occurs at time of infection or exposure to certain drugs

  • Common drugs initiating hemolysis

    • Dapsone

    • Methylene blue

    • Phenazopyridine

    • Primaquine

    • Rasburicase

    • Toluidine blue

    • Nitrofurantoin

    • Trimethoprim/sulfamethoxazole

    • Sulfadiazine

    • Pegloticase

    • Quinolones

  • Hemolytic episode self-limited, even with continued use of offending drug, because older RBCs (with low G6PD activity) are removed and replaced with young RBCs (with adequate G6PD activity)

  • Chronic hemolytic anemia in severe G6PD deficiency (eg, Mediterranean variants)


  • Blood is normal between hemolytic episodes

  • Hemoglobin rarely falls below 8 g/dL, though reticulocytosis and increased indirect bilirubin occur during hemolytic episodes

  • G6PD enzyme assays are low, especially in severe cases of G6PD deficiency

  • G6PD enzyme assays may be falsely normal if performed during or shortly after hemolytic episode during the period of reticulocytosis

  • Peripheral blood cell smear, although not diagnostic, may reveal bite cells and blister cells

  • Heinz bodies may be seen on peripheral blood smear stained with cresyl violet


  • Avoid known oxidant drugs

  • Otherwise, no treatment necessary

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