The basic principle of transfusion states that if the cells of the blood to be transfused will be agglutinated by the recipients plasma, the transfusion must not be made. Thus, since the cells of a group. A blood are agglutinated by B plasma, A blood cannot be given to a B patient.
On the other hand, the cells of O blood are not agglutinated by any plasma, therefore O blood can be given to patients with other types of blood. Accordingly, the individuals with O blood are termed universal donors. The plasma of AB blood does not agglutinate the cells of any blood. Hence, the individuals with this type of blood are termed universal recipients.