The transfer of blood or blood products from one person (the donor) into another person (the recipient's) bloodstream. In most situations, this is done as a lifesaving maneuver to replace blood cells or blood products lost through severe bleeding. Transfusion of your own blood (autologous) is the safest method but requires planning ahead and not all patients are eligible. Directed donor blood allows the patient to receive blood from known donors. Volunteer donor blood is usually most readily available and, when properly tested has a lower incidence of adverse events.