ABSTRACT
In biochemical terms, methemoglobin (MetHb), or ferrihemoglobin, is an oxidation product and chemical analog of the normal blood pigment hemoglobin (1). When iron is oxidized from the ferrous state in hemoglobin to the ferric state, methemoglobin is produced (2). Oxygen bound to methemoglobin is so firmly attached that it is not available to tissues; consequently, methemoglobin is not an oxygen-transporting pigment (3). Methemoglobin is normally present in a low concentration in red blood cells; total blood pigment is usually about l%-2% methemoglobin and the remainder is hemoglobin, with iron in the normal reduced state (3-5). The percentage of methemoglobin is the ratio of methemoglobin to hemo globin. For example, a methemoglobin concentration of 50% means that in a patient with 16 g of hemoglobin 8 g is methemoglobin. The percentage can therefore be mis leading, especially in the presence of anemia (6).
