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[Gr. meta, across, + haima, blood, + L. globus, globe]
SYMB: metHb. A form of hemoglobin in which the ferrous iron has been oxidized to ferric iron. Methemoglobin cannot transport oxygen. The presence of metHb in the blood may be due to toxic substances such as aniline dyes, potassium chlorate, or nitrate-contaminated water and to atypical responses to benzocaine-like analgesics, among other causes. Methemoglobin also is present in patients with a hereditary deficiency of methemoglobin reductase.

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