methaemoglobin

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Related to Hemiglobin: Hemoglobin A1c

methaemoglobin

methaemoglobin

A haemoglobin that results when oxyhaemoglobin in a ferrous (Fe2+) state is transformed into a ferric (Fe3+) state, which cannot transport O2. Low levels of methaemoglobin are always present in the circulation, but markedly increase after exposure to certain anaesthetics, benzocaines, nitrates, nitrites, phenacetin, etc., resulting in methaemoglobinaemia.
 
Ref range
• Normal, < 3% total MetHb.
• Cyanosis, 10–20% MetHb.
• Anoxia > 30% MetHb.

Specimen
Serum in sodium heparin (green top tube).
 
Method
Spectrophotometry.

met·he·mo·glo·bin

(metHb) (met-hē'mŏglō'bin)
A transformation product of oxyhemoglobin because of the oxidation of the normal Fe2+ to Fe3+, thus converting ferroprotoporphyrin to ferriprotoporphyrin; useless for respiration; found in bloody effusions and in the circulating blood after poisoning with acetanilid, potassium chlorate, and other substances.
Synonym(s): hemiglobin, methaemoglobin.

methaemoglobin

HAEMOGLOBIN that has been altered by oxidation of the iron fraction from the ferrous to the ferric state by drugs such as PHENACETIN, DAPSONE and related compounds or by nitrites. It is of a brown colour and does not combine reversibly with oxygen.