Methemoglobinemia overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Methemoglobinemia (congenital or acquired) is a blood disorder in which, due to increased production, the red blood cells (RBCs) contain abnormal hemoglobin, called methemoglobin (MetHb) at levels higher than 1%. The formation of methemoglobin results from the substitution of iron (Fe) in ferric (Fe2+) form, as found in normal hemoglobin, with iron in a reduced (Fe3+) form. Hemoglobin is a polypeptide protein in red blood cells (RBCs) that binds, carries and distributes oxygen from the lungs to the tissues, consisting of 2 alfa and 2 beta chains, connected to an iron atom in ferric form. In MetHb the ability of hemoglobin to bind oxygen is decreased and whatever oxygen does bind to the MetHb, is so tightly held, that very little oxygen actually gets released to the tissues, which leads to hypoxia and dyspnea.
Historical Perspective
Classification
Congenital (Hereditary) Methemoglobinemia
There are three main congenital conditions that lead to methemoglobinemia:
1. Cytochrome b5 reductase deficiency and pyruvate kinase deficiency
2. G6PD deficiency
3. Presence of abnormal hemoglobin.
Acquired or Acute Methemoglobinemia
The most common causes are different oxidant drugs, toxins and chemicals.