Blood transfusion is the procedure of transferring blood into the vein of a human recipient. This can be done by taking blood from a blood bank or directly from a donor. In general, a blood transfusion is a therapeutic option to help restore the volume of plasma or blood after severe trauma or injuries. Also, it can treat shock and increase the concentration and number of red blood cells, which can improve the capacity of carrying oxygen in the blood of people with anemia. This procedure plays an important role in some forms of surgery in which a large amount of blood should be replaced.