Haemoglobin transports oxygen from the pulmonary capillaries to vital organs and other tissues. Acute anaemia, for example as a consequence of surgical blood loss, can lead to tissue hypoxia and organ damage. When haemoglobin concentration drops below critical levels, red blood cell (RBC) transfusion may be indicated and even lifesaving. However, RBC transfusion has also been associated with many complications, for instance transfusion reaction, infection transmission, and acute lung injury. Therefore, determining adequate transfusion triggers is of utmost importance.¹ The prevailing Dutch transfusion guideline endorses the ‘4-5-6’ strategy, in which patient characteristics and clinical status influence the decision to apply RBC transfusion.² In short, RBC transfusion is triggered by haemoglobin concentrations below 4 mmol/L in healthy adults, whereas this trigger is 6 mmol/L in cardiopulmonary restricted patients. Despite its simplicity, recent evidence suggests that the ‘4-5-6’ strategy does not benefit patient outcomes and that a more restrictive use of RBC transfusion might be beneficial. A recent, multicenter, randomized study comprising of more than five thousand cardiac surgery patients found no difference in clinical outcomes (stroke, renal failure, myocardial infarction and death) between a transfusion trigger of 4.5 and 6 mmol/L , respectively.³ Furthermore, a randomized study comprising of almost one thousand patients with acute upper gastrointestinal bleeding found an higher survival rate with a transfusion trigger of 4.3 compared to 5.5 mmol/L.^1-4 Therefore, we expect that future guidelines will recommend restrictive use of RBC transfusion in critical care settings.