Washington, Aug 7 - Blood transfusion to hospitalised cardiac patients doubles the risk of infection and quadruples the risk of death, according to a new study.

The analysis of nearly 25,000 'Medicare' patients in Michigan also showed that transfusion practices after heart surgery varied substantially among hospitals, a red flag that plays into the health care reform debate.

Blood transfusions are extremely common in the US. Some of the typical reasons for transfusions include prevention of anaemia and improving oxygen delivery in heart failure.

Blood transfusion is an area that could be well served with stronger, research-based guidelines, since the current clinical practice is all over the map, said study co-author Neil Blumberg, professor of pathology at the University of Rochester Medical Centre (URMC).

'Doctors are simply doing what they were trained to do, but it turns out that their actions are more harmful than helpful in many cases,' Blumberg said.

'This is an instance in which clinical practice got way ahead of research.