Blood banks and blood centers are used to store blood that has been given by donors for future transfusions. They exist in both health and hospital centers, as well as mobile donation centers that can be transported to and from various donation events as a means of being more accessible to the blood-giving public. Bone marrow donations are also possible and stored at these centers.
Blood transfusions are used in a wide variety of medical situations and emergencies and can be life-saving. They involve the intravenous delivery of necessary components, like white cells, plasma, red cells, and platelets, can only be completed with blood that is a match with the patient's own blood type. Infusion of the incorrect blood type in a patient can result in organ failure.
Donating blood is very simple. At the donation site, a brief background check is conducted to evaluate your medical history to make sure that your donation will be safe to use in the event it is picked for a transfusion. They lay you on a bed and sterilize the injection site on your arm. A single needle is inserted in your arm, and over the course of a couple of minutes you donate a pint of blood. Sometimes they will have you squeeze your hand in order to improve circulation and increase flow to the donation bag. After, you are given water and a small snack to re-hydrate you and give you energy. On occasion someone will faint, but this is rare. If only your blood plasma is needed, the separation of the blood's components usually occurs after the donation is complete. Donor's can also donate bone marrow, a much more involved process.
The donations are then stored at a blood bank at a very specific temperature until they are needed.