Abstract
Cow's milk protein allergy (CMPA) is the most common food allergy in infants. A previously healthy neonate fed with infant formula presented diarrhoea, vomiting and respiratory distress with cyanosis. Investigations showed thrombocytosis and leucocytosis with lymphocyte predominance. To our surprise blood gas analysis showed metabolic acidosis and a high methaemoglobin level of 33% (normal range <3%). Clinical status, metabolic acidosis and methaemoglobin level returned to normal following fluid resuscitation and methylene blue administration. The neonate was later managed with breast feeding and elemental formula. CMPA was diagnosed based on history and clinical improvement after elemental formula. Although not common in CMPA, methaemoglobinaemia should be recognised as a differential diagnosis in a hypoxic infant with metabolic acidosis and diarrhoea as early recognition and treatment with methylene blue can save a child's life.