People come in all different shapes, sizes and blood types.
Your blood type depends on the makeup of your red blood cells, shown here, which carry oxygen to all tissues of the body. A person's blood type depends on the presence or absence of specific substances on the surface of red blood cells. Red blood cells are the portion of blood responsible for carrying oxygen throughout the body. These substances, called antigens, are made of mostly protein and carbohydrates and differ from person to person. However, there are more than 600 known antigens besides A and B that characterize the proteins found on a person's red cells.