What is methemoglobinemia characterized by?

Methemoglobinemia is characterized by the excessive production of methemoglobin, which is an altered form of hemoglobin. In this condition, the iron in hemoglobin is oxidized from the ferrous (Fe2+) to ferric (Fe3+) state, preventing the hemoglobin from effectively binding to oxygen. This results in a reduced ability of the blood to carry oxygen to the tissues, leading to symptoms such as cyanosis (a bluish discoloration of the skin), fatigue, and shortness of breath.

The primary issue in methemoglobinemia is this abnormal accumulation of methemoglobin, which is why option A accurately reflects the hallmark of this condition. Other options do not directly describe the main characteristic of methemoglobinemia and refer to different blood-related issues, making them less relevant to the defining aspects of this condition.