Blood transfusion is the process of transferring blood or blood products into one's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. It may need a blood transfusion if you have: A severe infection or liver disease that stops your body from properly making blood or some parts of blood. An illness that causes anemia, such as kidney disease or cancer. Medicines or radiation used to treat a medical condition also can cause anemia. Blood Transfusion. A blood transfusion is a common, safe medical procedure in which healthy blood is given to you through an intravenous (IV) line that has been inserted in one of your blood vessels