Blood products

[Monty]

People are sometimes given transfusions of whole blood during severe bleeding (for example after an injury or pregnancy complications), but usually they are given only the blood component they need. The different components of blood include

Red blood cells
Platelets
Plasma
White blood cells

Plasma contains antibodies (immunoglobulins) and clotting factors, which are sometimes separated from plasma.
Not all components are produced from a particular unit of donated blood. For example, immunoglobulins and clotting factors may be prepared from plasma pooled together from many donors. White blood cells and platelets are obtained by apheresis. Depending on the situation, people may receive only the red blood cells, platelets, plasma, or cryoprecipitate. Transfusing only selected blood components allows the treatment to be specific, reduces the risks of side effects, and can efficiently use the different components from a single unit of blood to treat several people.
Sometimes blood products are treated with radiation to reduce the risk of the transfused white blood cells attacking the recipient (graft-versus-host disease).
Some blood products can be treated with a chemical that reduces the risk of transmission of infection-causing microorganisms. In this procedure, called pathogen reduction technology, certain blood products are treated with a chemical that reduces the risk of transmission of almost all microorganisms.

[Sommer]

Whole blood can provide improved oxygen-carrying capacity, volume expansion, and replacement of clotting factors and was previously recommended for rapid massive blood loss. However, because component therapy is equally effective and is a more efficient use of donated blood, whole blood is not generally available in the US.