ABC of transfusion. Immunological complications of transfusion.

or pregnancy (Rh+ fetus) The transfusion of blood or its components can correct many deficiencies, even if only temporarily, and in most cases this effect can be achieved without any untoward effects. Nevertheless, incompatibilities of several kinds do occasionally cause trouble. Each blood cell has many different antigens on its surface, so the cells of a donor are virtually certain to contain antigens different from those of the recipient. In addition, the donor's plasma may contain proteins that are foreign to the recipient. Fortunately the transfusion of blood cells or plasma containing foreign antigens causes an immediate reaction only when the recipient's serum contains a corresponding antibody. In practice, severe reactions (caused, for example, by transfusion of incompatible red cells) are rare, whereas mild reactions (caused, for example, by reactions to foreign protein and characterised by urticaria) are common. For two reasons antibodies to red cell antigens are the most important in blood transfusion. Firstly, the volume of red cells transfused is usually greater than that of white cells or platelets so that if incompatible red cells are transfused the consequences are comparatively severe. Secondly, antibodies evoked by transfusions in women of childbearing age may subsequently cause haemolytic disease in their offspring.