In this study, von Heymann and colleagues describe the effects of different degrees of preoperative anaemia and/or transfusion on long-term survival. The most striking finding of this investigation is the calculation of the hazard ratios for long-term mortality depending on anaemia and/or transfusion. For all degrees of anaemia, long-term survival was worse in patients who presented with anaemia and received a transfusion compared with those who did not receive a transfusion.
At first sight, this finding suggests causality for both risk factors; however, it has to be stated that the third player of the unhappy triad, “anemia, bleeding and transfusion”, has not been mentioned. It remains unclear (as stated in the discussion) whether the reason for transfusion was acute bleeding or just a low haemoglobin value. This might considerably influence the results because it could be speculated that the patients transfused were those who experienced bleeding, a clinical situation which is also known to be an independent risk factor for worse outcomes. In that case, transfusion would not be an independent risk factor for mortality but rather a dependent variable associated with bleeding.
– Jens Meier