A blood transfusion is a medical procedure in which you receive whole blood or blood parts through a vein (intravenously). You may need a blood transfusion if you have an injury or illness that causes you to lose large amounts of blood, or if your body isn't making enough blood. Blood transfusions can also help treat certain illnesses, including sickle cell disease and other blood disorders. Blood used in transfusions is screened by blood banks to make sure it is safe for use. Follow the links below to find WebMD's comprehensive coverage about blood transfusions, why you might need one, how it is done, the possible risks, and more.