Trauma

• Traumatic injury that produces a great deal of blood lose must be treated with a blood transfusion. When the blood supply dips dangerously low due to a traumatic injury, the body goes into shock which can be fatal if the blood supply is not restored. Blood transfusions are used to restore the blood supply in such cases.
  
  

Surgery

• Surgery patients can lose a great deal of blood during an operation. To keep the body from going into shock, many patients receive blood transfusions while they are still on the operating table. Surgery patients usually receive full blood transfusions to restore the blood supply just like traumatic injury patients. According to the American Heart, Lung and Blood Institute, nearly one in three heart surgery patients need a transfusion during their surgery.
  
  

Clotting Disorders

• Individuals who have clotting disorders such as hemophilia often require blood transfusions. Because their blood lacks the factor needed to stop bleeding, even a minor injury can cause a great loss of blood. Hemophiliacs will receive many blood transfusions throughout their life, and internal injuries from falls or accidents can be a cause of great concern. In a hemophiliac, fresh, healthy blood is used to restore the blood flow and help the body clot when necessary.
  
  

Anemia

• Anemia occurs when the blood does not produce enough iron and it can cause illness and general feelings of being unwell. Anemia is caused by a number of different ailments, but those with kidney problems most commonly receive blood transfusions that restore the iron level in the blood and help patients to feel better as they deal with the underlying illness.
  
  

Cancer

• Cancer patients who undergo radiation often end up with anemia as a side effect. Blood transfusions are used in such cases to restore normal levels in the blood and create a healthier body that can undergo and deal with radiation and chemotherapy better. Cancer patients may not receive full blood transfusions but rather are often transfused with certain parts of the blood, such as platelets.