There are approximately eight million volunteer blood donors. About four million patients receive transfusions of blood units each year. Each unit of blood is broken down into components, such as red blood cells, plasma, and platelets. One unit of whole blood, once separated, may be transfused to several patients, each with different needs. Annually, more than 23 million units of blood components are transfused.
Most blood donors are volunteers.
Donating blood for yourself is called an autologous donation. Some states permit persons younger than 17 years to donate blood with parental consent. I rradiation to blood cells is performed to disable any T-lymphocytes present in the donated blood. Leukocyte reduced blood has been filtered to remove the white blood cells which contain antibodies that can cause fevers in the recipient of the transfusion. Plasma is needed to carry the many parts of the blood through the bloodstream.