Methemoglobinemia is a condition in which there is an abnormal increase in the level of methemoglobin, a form of hemoglobin in which the iron ion in the heme group is oxidized from the ferrous (Fe²⁺) to the ferric (Fe³⁺) state. Methemoglobin does not effectively bind or release oxygen, and as a result, methemoglobinemia can lead to functional anemia and a reduced ability to transport oxygen to tissues. The normal hemoglobin present in the blood can still bind and transport oxygen, but if the levels of methemoglobin are too high, it can result in not enough oxygen getting to the tissues. In severe cases, methemoglobinemia can be life-threatening.