Persistent cyanosis in a 4 month old infant with severe pneumonia and haemoglobin M.

M haemoglobinaemia is a rare cause of persistant cyanosis. We report a four months old infant who suffered from severe pneumonia and respiratory distress syndrome. After return of normal respiration, cyanosis persisted. Oxygen saturation on pulse oximetry never exceeded 85%. Finally, we succeeded in isolating a haemoglobin M Saskatoon. HbM Saskatoon is normally a harmless variant. However, in conjunction with severe pneumonia, we assume that it did not only affect clinical evaluation, but also exacerbated pneumonia by reducing the oxygen binding capacity.