methaemoglobin


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Related to methaemoglobin: carboxyhemoglobin, Blue baby syndrome

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.
References in periodicals archive ?
Due to exposure to drugs and chemicals commonly used in cardiac and anaesthetic procedures, which oxidizes haemoglobin to form methaemoglobin. [7]
The addition of ascorbic acid to nitrateamendedtissues changesblood andbiochemical parameters as well.These results indicated that ascorbic acid can reduce methaemoglobin [21] ormay augment the function of endogenous free radical scavengers and decreases the adverse effect of nitrates on body cells [7].
We have revealed characteristic changes in clinical laboratory parameters--increased lipid peroxidation, decreased AOA in the blood and superoxide dismutase activity, increased MDA and methaemoglobin levels, mild inflammatory changes on the complete blood count with no clinical signs of disease exacerbation, reduced non-specific resistance, the imbalance of cellular and humoral immunity, suggesting a long-term antigenic stimulation, restructuring of the receptors of immunocompetent cells, the inhibition of the receptor CD56+ expression, which reduces the antiviral and anti-tumor immunity.
Several screening tests are available such as dye decolourization test, monospotflurorescent test, methaemoglobin reduction test and formazan test.
These analysers are equipped with a cooximeter, which enables determination of bilirubin and various forms of haemoglobin (the total, oxy-, carboxy-, sulpho-, and methaemoglobin).
The red cell nicotinamide adenine dinucleotide hydrogen (NADH) dependent methaemoglobin reductase or diaphorase I enzyme (Breaking et al., 1951; Gibson and Harrison, 1947), protects the erythrocyte from an accumulation of methaemoglobin.
After nitrite absorption through fish gills it reacts with the hemoglobin iron in the blood, converting it in methaemoglobin which is not capable to transport oxygen.
When carbon monoxide combines with haemoglobin it forms carboxyhaemoglobin and methaemoglobin which reduces the oxygen-carrying capacity of the blood and can result in hypoxic stress (Alp et al 2006).
People who suffer from methaemoglobinaemia have high blood methaemoglobin concentration with usual symptoms like cyanosis, headache, dizziness, shortness of breath, and loss of consciousness.
Arterial blood gas analysis showed oxygen saturation of 98%, pH 7.36, [P.sub.a]C[O.sub.2] 26 mmHg, [P.sub.a][O.sub.2] 123 mmHg, bicarbonate 14 mmol/l, lactate 8.5 mmol/l and methaemoglobin level 46.8%.
Carboxyhaemoglobin and methaemoglobin findings in burnt bodies.