DefinitionMethemoglobinemia is a blood disorder in which an abnormal amount of hemoglobin builds up in the blood. Hemoglobin is the oxygen-carrying molecule found in red blood cells. In some cases of methemoglobinemia, the hemoglobin is unable to carry oxygen effectively to body tissues.Alternative NamesHemoglobin M disease; Erythrocyte reductase deficiency; Generalized reductase deficiencyCauses, incidence, and risk factorsMethemoglobinemia may be passed down through families (inherited). Or, it may result from 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 the