A blood transfusion is a routine medical procedure in which donated blood is provided to you through a narrow tube placed within a vein in your arm. This potentially life-saving procedure can help replace blood lost due to surgery or injury. A blood transfusion also can help if an illness prevents your body from making blood or some of your blood's components correctly. Blood transfusions usually occur without complications. When complications do occur, they're typically mild. People receive blood transfusions for many reasons — such as surgery, injury, disease and bleeding disorders. Blood has several components, including: Red cells carry oxygen and help remove waste products, White cells help your body fight infections, Plasma is the liquid part of your blood, Platelets help your blood clot properly transfusion provides the part or parts of blood you need, with red blood cells being the most commonly transfused. You can also receive whole blood, which contains all the parts, but whole blood transfusions aren't common. Researchers are working on developing artificial blood. So far, no good replacement for human blood is available.