Congenital Methemoglobinemia

Sumit Larokar, Preetham Manoli, Maneesha Halkar, Ranjan Kumar Pejaver


Congenital methemoglobinemia is an inborn error of metabolism, which may or may not be familial. Normal range of methemoglobin (metHb) is 0.01% to 1%. The enzyme system which regulates the balance between hemoglobin (Hb) containing iron in the ferrous state and metHb containing iron in the ferric state is disturbed. Cyanosis is a significant clinical feature of the disease and is usually present in varying degrees. The administration of methylene blue or ascorbic acid (vitamin C) decreases metHb level.

Administration of methylene blue is the treatment of choice for severe methemoglobinemia. In the presence of nicotinamide adenine dinucleotide phosphate, methylene blue is converted to leucomethylene blue, which results in nonenzymatic reduction of metHb. Ascorbic acid directly reduces metHb, but the rate of reaction is too slow for it to be effective when used alone. A combination of methylene blue and ascorbic acid is also used sometimes; if this combination fails to reduce the metHb level, then hyperbaric oxygen and exchange transfusions are alternative therapies.

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