Blood carries gases, nutrients and waste products through the body. Blood also fights infections, heals wounds and performs many other vital functions.
There is no substitute for human blood. It cannot be made or manufactured, and patients rely on volunteer blood donors. Volunteer blood donors are the only source of blood for patients who need blood transfusions. Blood contains a number of different components, and doctors use component transfusions to give patients exactly what they need.
There are four main blood types: O, A, B and AB
The blood type of a donor determines who can receive their donation.
To learn more about the history and biology of blood, visit America's Blood Centers.