What is methemoglobin?

Methemoglobin is characterized as a form of hemoglobin in which the iron within the heme group is in the ferric state, meaning it is oxidized to Fe3+. Under normal circumstances, hemoglobin contains ferrous iron (Fe2+), which is essential for binding oxygen effectively. However, when hemoglobin is converted to methemoglobin, the ability to bind oxygen diminishes because ferric iron does not have the capacity to carry oxygen. This condition can result from various factors, including exposure to certain chemicals or medications, and can lead to a decrease in the oxygen-carrying capacity of the blood.

The oxidation of iron to the ferric state is central to understanding methemoglobin's impact on oxygen transport in the body. Therefore, recognizing methemoglobin as hemoglobin with ferric iron is crucial for identifying potential clinical conditions associated with its increased levels.