methaemoglobin

Methemoglobin is a form of hemoglobin in which the iron atom is in the ferric (Fe3+) state, rather than the normal ferrous (Fe2+) state. Hemoglobin is the protein in red blood cells responsible for transporting oxygen from the lungs to the body's tissues. In methemoglobin, the iron's oxidation state prevents it from binding to oxygen effectively, thus reducing the oxygen-carrying capacity of the blood.

Normally, there are very small amounts of methemoglobin present in red blood cells, which are quickly reduced back to normal hemoglobin by enzymes like cytochrome b5 reductase. However, elevated levels of methemoglobin can be caused by genetic defects or exposure to certain substances. These substances, known as oxidizing agents, can include certain medications (like some anesthetics and antibiotics), chemicals (such as nitrates and aniline dyes), and environmental toxins.

Symptoms of methemoglobinemia, the condition characterized by elevated methemoglobin levels, depend on the concentration. Mild cases might present with bluish discoloration of the skin and mucous membranes (cyanosis), headache, and fatigue. More severe cases can lead to shortness of breath, dizziness, confusion, seizures, and even death if left untreated. Diagnosis is typically made by measuring methemoglobin levels in a blood sample. Treatment involves removing the causative agent and, in severe cases, administering methylene blue, which acts as a cofactor to help reduce methemoglobin back to functional hemoglobin.