In medicine, ABO refers to the ABO blood group, which can be specifically categorized as type A, B, AB and O. ABO blood type is the most clinically used blood type, which is categorized according to the antigens on the red blood cells. If the red blood cells have A antigens on them, then it is A blood type. If the red blood cells have the A antigen, then it is blood type A. If they have the B antigen, then it is blood type B. If it has both A and B antigens, it is blood type AB, and if it has neither antigen, then it is blood type O. During blood transfusion, the principle of isotype transfusion is generally observed, which can prevent severe hemolysis from affecting a person’s health.