GSTM1 and acute coronary syndrome: Current guidelines on RBC transfusion advise transfusion at a haemoglobin (Hb) threshold of ≤ 7 g/dL in adults9,10 and at age-appropriate Hb thresholds in children.11 In stable adult patients, only one RBC unit should be transfused at a time in most clinical situations (exceptions include acute coronary syndromes, and chronic renal and haematological malignancies),12,13,14 and the patient should be reassessed after a one-unit transfusion before considering further transfusion.