A child with respiratory distress and chocolate brown arterial blood

Methemoglobinemia is a hemoglobinopathy that occurs when the heme is oxidated. Ferric iron in oxidized heme cannot bind and transport oxygen. Hence, when the concentration exceeds 15%, symptoms start with cyanosis, distress, and tachypnea, and may progress to seizure, unconsciousness, and even death as the concentration increases. Congenital methemoglobinemia is rare and often clinically missed but responds well with medications. Here, the case of a 12-year-old girl with respiratory distress and no cyanosis is being reported. The diagnosis was made based on a chocolate brown-colored arterial blood sample taken for analysis. The importance of considering this condition as a differential diagnosis in a case of respiratory distress of unknown etiology is being discussed here.