In cases where an individual has lost whole blood by hemorrhaging, it is often necessary to give transfusions of whole blood.
Whole blood transfusions continue the functions of the RBCs.
On the other hand, if an individual has suffered burns causing a loss of fluid but not the loss of formed elements, plasma or a plasma substitute will often be used.
There are a number of substances (antigens) on the surfaces of RBCs that vary among individuals.
The blood of other individuals may contain or develop antibodies to these antigens.
Before blood transfusions, the blood of the recipient and the donor must be matched to avoid potentially fatal reactions.
Important systems of such antigens include the ABO system and the Rh system.