methemoglobin
Meaning of methemoglobin: Methemoglobin is a chemically altered form of hemoglobin that cannot bind oxygen, and it is normally present in blood only in small amounts.
Definition of methemoglobin
Methemoglobin is a form of hemoglobin, the oxygen carrying protein in red blood cells, in which the iron within the molecule has been chemically altered so that it can no longer bind oxygen. A small amount of methemoglobin is normally present in the blood at all times.
Certain medications, chemicals, and foods can increase the rate at which hemoglobin converts to methemoglobin, or can overwhelm the body's normal ability to convert methemoglobin back to its oxygen carrying form, allowing methemoglobin to accumulate beyond its usual small amount.
When methemoglobin makes up a large enough share of total hemoglobin, the blood's capacity to deliver oxygen to tissue falls, a condition called methemoglobinemia, and this can be identified through blood testing that distinguishes methemoglobin from normally functioning hemoglobin.
Used in a sentence
Laboratory testing measured the proportion of methemoglobin relative to total hemoglobin.
Good to know
A small amount of methemoglobin is a normal finding in blood and does not by itself indicate methemoglobinemia, since that diagnosis depends on the proportion of total hemoglobin it represents.
Word origin
Where “methemoglobin” comes from
Formed from Greek meta-, meaning change or beyond, combined with hemoglobin, itself from Greek haima, meaning blood, and Latin globus, meaning ball.