methemoglobin

Methemoglobin is an altered form of hemoglobin where the iron component is oxidized, rendering it unable to transport oxygen. This leads to a decrease in the oxygen-carrying capacity of red blood cells, a condition known as methemoglobinemia. Symptoms can range from a bluish discoloration of the skin and mucous membranes to more severe issues like weakness and difficulty breathing.12

Normally, enzymes keep hemoglobin's iron in a reduced state for oxygen binding. Methemoglobinemia can be hereditary, caused by enzyme defects or abnormal hemoglobin structure, or acquired through exposure to certain drugs and chemicals that promote iron oxidation. Treatment for hereditary cases may involve reduction compounds like methylene blue, while acquired cases often resolve when the causative agent is removed. Sulfhemoglobinemia is a related condition involving irreversible sulfur binding to hemoglobin, also impairing oxygen transport.13