Each year in Britain 2.2 million units of red cells are transfused and perhaps four deaths due to preventable causes subsequently occur. Providers of health care and the public express most concern about the risk of infections transmitted by transfusion, particularly HIV infection, but procedural errors resulting in ABO incompatibility cause most of the deaths immediately after blood transfusion.^1,2 ABO antibodies are “naturally occurring” and are present in all subjects except those of blood group AB after the first 3 to 6 months of life. Although these antibodies can cause intravascular haemolysis, with disseminated intravascular coagulation and renal failure, most incompatible transfusions are uneventful or result in minor signs and symptoms.^3,4 Only about 1 in 10 ABO incompatible transfusions is fatal.2

Studies in the United States, where all deaths associated with transfusions must be reported to the Food and Drug Administration, show that patients with blood group O are most at risk of dying from ABO incompatibility^1,2 because they have the highest concentrations of potent antibodies directed against A and B antigens. Other causes of death from transfusions, excluding viral infections, are generally not preventable. They include, in order of frequency of reports, acute lung injury related …