This is to make sure that blood given to you is compatible with your own blood. In an extreme emergency, blood type O, known as the universal donor, will be given as a lifesaving measure. In addition to testing of the patient's blood, ALL donated blood is screened for the AIDS virus, the hepatitis B virus, as well as other infecting agents. During surgery for brain tumors, some people require a blood transfusion. Transfusions may also be required if radiation or chemotherapy reduces the bone marrow's production of new blood.
Red cells carry oxygen from the lungs to the rest of the body, so they are very important.
Lack of red blood cells causes anaemia. You may feel tired, fatigued or weak. These cells may need to be replaced with a packed red blood cell transfusion. White blood cells are the major response by the immune system to infection. We are constantly exposed to bacteria or viruses which could make us quite ill but our immune system fights them off.