Abstract We report a very rare case of methaemoglobinaemia associated with glucose 6 phosphate dehydrogenase (G6PD) deficiency, complicating a respiratory illness in a preterm neonate. This neonate had consistently low saturation readings despite being ventilated at moderately high
pressures in 100% oxygen. An arterial blood gas confirmed a high methaemoglobin level and a high pO2, inconsistent with the saturations. In addition, the bilirubin increased to exchange levels and was difficult to control with quadruple phototherapy. A double volume exchange transfusion
was performed, which reduced both bilirubin and methaemoglobin. The pulse oximetry then started to correlate well with pO2. G6PD deficiency was confirmed. Conclusion: Paediatricians should remember that methaemoglobinaemia is a rare but important cause of persistently low saturations,
and exchange transfusion is a reliable treatment for this condition.