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Methemoglobinemia

Key sources
The following summarized guidelines for the evaluation and management of methemoglobinemia are prepared by our editorial team based on guidelines from the American Heart Association (AHA 2023) and the European Hematology Association (EHA 2021).
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Guidelines

1.Screening and diagnosis

Screening of family relatives: test first-degree relatives of patients with hereditary methemoglobinemia.
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2.Diagnostic investigations

Clinical assessment
Assess clinical findings and elicit family history to distinguish acquired from inherited forms of methemoglobinemia.
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Recognize the neurologic and cardiac symptoms and their progression with increasing methemoglobin.
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  • Methemoglobin levels

  • Testing for NADH-cytochrome b5 reductase deficiency

  • Testing for G6PD deficiency

3.Respiratory support

Oxygen supplementation: administer oxygen supplementation if needed in minimally symptomatic or asymptomatic patients. Obtain routine monitoring of oxygen saturation with pulse oximetry in case oxygen is initiated, at least in neonates.
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  • Hyperbaric oxygen therapy

4.Medical management

General principles: manage methemoglobinemia in pediatric patients based on the symptoms, level of methemoglobin, cause of methemoglobinemia, and patient's age.
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  • Methylene blue

  • Ascorbic acid

  • N-acetylcysteine

5.Therapeutic procedures

Exchange transfusion: as per AHA 2023 guidelines, consider performing exchange transfusion in patients with methemoglobinemia not responding to methylene blue.
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  • Therapeutic phlebotomy

6.Perioperative care

Perioperative care: identify potential precipitating and exacerbating factors before surgery.
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7.Specific circumstances

Pregnant patients: ensure a multidisciplinary decision for methylene blue treatment during pregnancy and discussed with the patient weighing the risk of hypoxia on the fetus and the teratogenic and other effects of methylene blue.
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8.Patient education

General counseling: advise avoiding precipitating factors in patients with known hereditary or acquired methemoglobinemia and in patients with a CYB5R3 heterozygous variant.
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9.Follow-up and surveillance

Indications for referral: refer patients with mild symptoms to specialized laboratories or directly to emergency units in case of more severe symptoms to establish methemoglobin levels and initiate treatment.
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