methemoglobin
Pronunciation: meth-EE-mo-glo-bin
An altered form of hemoglobin containing ferric iron that cannot effectively carry oxygen, potentially causing cyanosis in infants.
Full Definition
Methemoglobin is a form of hemoglobin in which the iron atom has been oxidized from the ferrous (Fe2+) to the ferric (Fe3+) state, rendering it incapable of binding and transporting oxygen effectively. In pediatric patients, methemoglobinemia can be congenital due to enzyme deficiencies or acquired through exposure to certain medications, foods, or chemicals. Infants are particularly susceptible due to their immature enzyme systems. Clinical manifestations include cyanosis that doesn't respond to oxygen therapy, and levels above 15-20% can cause significant symptoms requiring immediate treatment with methylene blue.
Usage
Usage note: May be abbreviated as metHb; distinguish from other hemoglobin variants in documentation.
In Context
- "The 6-month-old infant's methemoglobin level of 22% explained the persistent cyanosis despite adequate oxygenation." — Emergency department note