The ABO blood grouping system is named primarily after the different aggrecogens, or blood group antigens, contained on the surface of human red blood cells. The ABO blood grouping system is the most commonly used blood grouping system in the clinic, and the classification of ABO blood groups is mainly based on the expression of antigen A and antigen B on the surface of the red cell membrane. According to the expression of erythrocyte membrane surface antigen, human blood type is divided into four types: type A, type B, type O and type AB. Blood type A is the expression of antigen A on the surface of erythrocyte membrane and the presence of antibody B in its serum.Blood type B refers to the expression of antigen B on the surface of erythrocyte membrane and the presence of antibody A in its serum.Blood type O refers to the surface of erythrocyte membrane that does not express antigen A or antigen B, and there are antibody A and antibody B in its serum.Blood type AB refers to the surface of erythrocyte membrane that expresses both antigen A and antigen B, and there is no antibody in its serum.