Methemoglobin (pronounced MET-hemoglobin) is a form of the oxygen-carrying protein hemoglobin (British English: haemoglobin), in which the iron in the heme group is in the Fe3+ state, not the Fe2+ of normal hemoglobin. Methemoglobin is unable to carry oxygen. It is chocolate-brown in color. The NADH-dependent enzyme methemoglobin reductase (AKA diaphorase I) is responsible for converting methemoglobin back to hemoglobin.
Normally one to two percent of people's hemoglobin is methemoglobin; a higher percentage than this can be genetic or caused by exposure to various chemicals and depending on the level can cause health problems known as Methemoglobinemia. A higher level of methemoglobin will tend to cause a pulse oximeter to read closer to 85% regardless of the true level of oxygen saturation.
- Reduced cellular defense mechanisms
- Children younger than 4 months exposed to various environmental agents
- Methemoglobin reductase deficiency
- G6PD deficiency
- Hemoglobin M disease
- Pyruvate kinase deficiency
- Various pharmaceutical compounds
- Local anaesthetic agents, especially prilocaine as used in the Bier block
- Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides
- Environmental agents
- Aromatic amines
Methemoglobinemia in infants
In children, this condition is known as blue baby syndrome, attributed primarily to excessive nitrate intake from drinking well water.
- Methemoglobin at the US National Library of Medicine Medical Subject Headings (MeSH)
cs:Methemoglobin da:Mæthæmoglobin de:Methämoglobin it:Metaemoglobina