Methemoglobinemia is a blood disorder in which an abnormal amount of methemoglobin -- a form of hemoglobin -- is produced. Hemoglobin is the molecule in red blood cells that distributes oxygen to the body. Methemoglobin cannot release oxygen.
In methemoglobinemia, the hemoglobin is unable to release oxygen effectively to body tissues.
Hemoglobin M disease; Erythrocyte reductase deficiency; Generalized reductase deficiency
Methemoglobinemia may be passed down through families (inherited or congenital). Or, it may be caused by exposure to certain drugs, chemicals, or foods (acquired).
There are two forms of inherited methemoglobinemia. The first form is passed on by both parents. The parents usually do not have the condition themselves, but they carry the gene that causes the condition. It occurs when there is a problem with an enzyme called cytochrome b5 reductase.
There are two types of this form of methemoglobinemia:
The second form of inherited methemoglobinemia is called hemoglobin M disease. It is caused by defects in the hemoglobin molecule itself. Only one parent needs to pass on the abnormal gene for the child to inherit the disease.
Acquired methemoglobinemia is more common than the inherited forms. It occurs in some people after they are exposed to certain chemicals and drugs, including:
The condition may also occur in infants who are very ill or who are fed too many vegetables containing nitrates (such as beets).
Symptoms of type 1 methemoglobinemia (erythrocyte reductase deficiency) include:
Symptoms of type 2 methemoglobinemia (generalized reductase deficiency) include:
Symptoms of hemoglobin M disease include:
Symptoms of acquired methemoglobinemia include:
Methemoglobinemia can be diagnosed with a blood test.
A medicine called methylene blue is used to treat severe methemoglobinemia. Note: Methylene blue may be dangerous in patients who have or may be at risk for a blood disease called G6PD deficiency, and should not be used. If you or your child has G6PD deficiency, always tell your health care provider before receiving treatment.
Ascorbic acid may also be used to reduce the level of methemoglobin.
In most cases of mild acquired methemoglobinemia, no treatment is needed. However, you should avoid the medicine or chemical that caused the problem. Severe cases may need treatment, which may include a blood transfusion.
People with type 1 methemoglobinemia and hemoglobin M disease usually do well. Type 2 methemoglobinemia is much more serious, and usually causes death within the first few years of life.
People with acquired methemoglobinemia usually do very well once the drug, food, or chemical that caused the problem is identified and avoided.
Call your health care provider if you have a family history of methemoglobinemia and you develop symptoms of this disorder.
Call your health care provider or emergency services (911) immediately if you have severe shortness of breath.
Genetic counseling is recommended for couples with a family history of methemoglobinemia who are considering having children.
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Fernandez-Frackelton M, Bocock J. Cyanosis. In: Marx JA, Hockberger RS, Walls RM, et al, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 7th ed. Philadelphia, Pa: Mosby Elsevier; 2009:chap 29.