Two Cases of Methemoglobinemia Secondary to Favism in Pediatric Patients With Unknown Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency predisposes to acute hemolytic crisis when exposed to oxidative stress. Methemoglobinemia occurs as a result of the oxidation of hemoglobin. This eventually affects the oxygen-carrying capacity of the red blood cells, resulting in hypoxemia. There is a reported association between the two conditions.  A 12-year-old boy with autism, with no history of hematologic disease, presented with acute hemolysis and respiratory distress. His arterial blood gas showed a methemoglobin level of 6.1%; he received methylene blue in the emergency department. The patient's condition deteriorated with a progressive drop in hemoglobin level. Laboratory investigations confirmed G6PD deficiency later on; it was then revealed that he had eaten fava beans one day before the symptoms. He required a blood transfusion, with an average stay of four days in the pediatric ICU, and eventually made a full recovery.  A 14-year-old boy, with short stature on growth hormone therapy and no history of hematologic disease, presented with acute hemolysis and respiratory distress one day after consuming Fava beans. His arterial blood gas showed a methemoglobinemia level of 7%; he was transfused and then transferred to another facility, where he received 4,000 mg of ascorbic acid in divided doses and multiple blood transfusions. Laboratory investigations confirmed G6PD deficiency. The patient required a blood transfusion, with an average stay of three days in the pediatric ICU, and eventually made a full recovery. The co-occurrence of methemoglobinemia with G6PD deficiency-related Favism is rare, with few reported cases in the literature. This association can be explained by the defective nicotinamide adenine dinucleotide phosphate-dependent pathway in G6PD deficiency. This pathway helps maintain iron in the ferrous form in the blood. The methemoglobinemia secondary to hemolysis in G6PD-deficient patients poses therapeutic challenges due to the lack of equally effective therapeutic options and the relatively long time to establish G6PD status, which may also result in false negatives in acute hemolysis. Methylene blue, the primary treatment of methemoglobinemia, is contraindicated. Ascorbic acid is considered to be a safer option and effective as an additive to blood transfusion in such cases.