People are the only source. The blood center does its part by asking you to donate, collecting, processing and delivering your blood to the hospitals around the clock. At least 580 blood donors are needed every day to take care of patients in local hospitals. The only way this enormous need can be met is by turning to the entire community. I gave once this year.
Blood is a living tissue and it dies if separated from the body.
Whole blood and red cells can be preserved up to 42 days. However, some parts of blood, such as the platelets that are necessary for clotting, survive only five days. To avoid shortages, donors must be recruited constantly. If anyone I know needs blood, I'll be the first to respond. It takes many hours from collection of a unit of blood through testing, typing and delivering.