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Case summary demonstrates critical diagnostic challenge of methemoglobinemia in G6PD deficient patient, suggesting recognition of saturation gap is essential.
Background: Methemoglobinemia is an uncommon but important cause of hypoxia characterized by a discrepancy between pulse oximetry and arterial oxygen tension. In glucose-6-phosphate dehydrogenase (G6PD) deficiency, oxidative stress may precipitate both hemolysis and methemoglobinemia. Case summary: An 18-year-old male presented with jaundice, dark urine, and acute hemolysis following probable ingestion of over-the-counter medications. He developed sudden hypoxia (SpO₂ 70%) without respiratory distress. Arterial blood gas revealed elevated PaO₂ (246 mmHg), indicating a saturation gap. Co-oximetry showed methemoglobin level of 21.1%. G6PD levels were reduced. Methylene blue was avoided, and the patient was treated with ascorbic acid, blood transfusion, and supportive care, resulting in recovery. Conclusion: Recognition of saturation gap is critical in diagnosing methemoglobinemia, especially in G6PD deficiency where standard therapy may be harmful.
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Jain et al. (2026) studied this question.
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