A transfusion (trans-few-zhun) is putting blood or some part of it in a vein through an intravenous (IV) line.
Transfusions of blood and blood products temporarily replace parts of the blood when a person has been bleeding, or when their body can’t make enough blood. The blood usually comes from another person, called a donor. Blood transfusions save millions of lives in the United States every year.
People usually donate whole blood – blood taken right out of a vein through a needle. This whole blood may be called a unit or pint of blood, and equals about 450 milliliters or 16.7 ounces. But whole blood is rarely given as a transfusion. Blood has many parts (components), such as red blood cells, white blood cells, platelets (plate-lets), plasma, clotting factors, and small proteins. Each component does a different job. After it’s donated, whole blood is usually separated into components. This lets doctors give patients only the part they need. It also helps to get the most out of the donated blood.