Transfusion is the process of transferring whole blood or blood components from one person (donor) to another (recipient), to restore lost blood, to improve clotting time, and to improve the ability of the blood to deliver oxygen to the body's tissues. Whole blood is used exactly as it was received from the donor. Blood components are parts of whole blood, such as red blood cells (RBCs), plasma, platelets, clotting factors, immunoglobulins, and white blood cells. Use of blood components is a more efficient way to use the blood supply, because blood that has been processed (fractionated) into components can be used to treat more than one person.

Whole blood is generally used when a person has lost a lot of blood by injury or surgical procedures and is given to help restore the blood volume, which is essential for maintaining blood pressure. Red blood cells are the blood...