This all matters if a person needs a blood transfusion (adding blood
to a person’s circulation, usually from another person), because in certain
combinations the blood cells will clump together. These clots cause potentially
fatal situations. In the ideal situation blood types are matched before the
transfusion takes place, but type O blood is often used in emergency situations
because it is usually accepted by all blood types.
Type A blood can be given to
type A or type AB.
Type B blood can be given to
type B or type AB.
Type
AB blood can be given only to another
type AB.
Type O can be given to all
other types.
Because type AB people can accept any other type, they are referred to as “universal
recipients.” Type O people are considered “universal donors.”