Methaemoglobinaemia

Key points

• Methaemoglobinaemia describes haemoglobin which has been oxidised from Fe2+ to Fe3+. This is normally regulated by NADH methaemoglobin reductase,
• haemoglobin chain variants: HbM, HbH
• NADH methaemoglobin reductase deficiency Acquired causes
• drugs: sulphonamides, nitrates, dapsone, sodium nitroprusside, primaquine
• chemicals: aniline dyes
• Management: stop the causative agent · IV METHYLENE BLUE (methylthioninium chloride) is the treatment for significant acquired methaemoglobinaemia · note the classic trap — methylene blue is ineffective and may precipitate haemolysis in G6PD deficiency, where ascorbic acid or exchange transfusion is used instead. Features