They found that patients who received a red blood cell transfusion experienced a three-fold increase in complications arising from lack of oxygen to key organs - such as in a heart attack or stroke.
The study also revealed that the risks associated with transfusion occurred regardless of the haemoglobin levels (the oxygen-carrying substance in red blood cells), age, or level of patient disability at the time of transfusion.
"Red blood cells carry oxygen around the body to supply vital organs. Not unreasonably therefore, heart surgeons have assumed that patients who have low red blood cell counts after surgery - as a result of blood loss during or shortly after surgery - would benefit from a 'top up' transfusion of donated red blood cells," said Professor Peter Weissberg, Medical Director at the BHF.
"This study shows the importance of putting such widespread beliefs to the test since it suggests that such transfusions may cause more problems than they solve. The results are a step towards making heart surgery even safer by flagging up an issue we can now address through research and improved transfusion guidelines," he added.
As well as the human costs, the financial cost of giving transfusions and treating transfusion-related illnesses increased the overall cost of staying in hospital by over 40 per cent.
Gavin Murphy, Walport Consultant Senior Lecturer in Cardiac Surgery at the University of Bristol, who led the study said: "This study demonstrates the cost implications of our current transfusion practice. This is important, particularly in modern health systems where resources are finite, and should encourage the sort of research that will address the major health issues raised in the study."
The research team is now looking forward to carry out a larger study to see if changing transfusion guidelines could improve patient outcomes. For the time being it is suggested that surgeons think twice before giving their patients a transfusion.
The new study is published in the November 27 of the journal Circulation.