Processing
Historically, blood was transfused as whole blood without further processing. Most blood banks now split the whole blood into two or more components, typically red blood cells and a plasma component such as Fresh Frozen Plasma. Platelets for transfusion can also be prepared from a unit of whole blood. Some blood banks have replaced this with platelets collected by plateletpheresis because whole blood platelets, sometimes called "random" platelets, must be pooled from multiple donors to get enough for a therapeutic dose.
The collected blood is generally separated into components by one of three methods. A centrifuge can be used in a "hard spin" which separates whole blood into plasma and red cells or for a "soft spin" which separates it into plasma, buffy coat (used to make platelets), and red blood cells. The third method is sedimentation: the blood simply sits overnight and the red cells and plasma are separated by gravity.
Read more about this topic: Whole Blood