how are blood types determined?
1 Everyone has one of four blood types â A, B, AB, or O â which is inherited from your parents. 2  Your blood type is determined by the presence or absence of two antigens â A and B â on the surface of red blood cells.A third antigen, called Rh factor, will either be present or absent. Antigens are substances that may trigger an immune response, causing your body to launch an attack if it believes they are foreign.hile all blood is similar in its components (such as containing red cells, platelets, and plasma), it also has important characteristics that make it unique. Your blood type is determined by the presence or absence of two antigens â A and B â on the surface of red blood cells.