Erythrocyte agglutination is a condition in which red blood cells are clustered together due to antigen-antibody reactions, and at the same time are destroyed by lysis of the red blood cells. Because different red blood cells contain different antigens on the red blood cell membrane, at the same time, different red blood cells also contain different antibodies in the serum, for example, in the ABO blood group system, type A blood contains type A antigens on the red blood cell membrane, and in the serum contains anti-B antibodies. type B blood also has type B antigens on the red blood cell membrane, and in the serum there are anti-A antibodies. When blood type A and blood type B are mixed, red blood cell agglutination occurs due to the antibody-antigen reaction. The red blood cells get together with each other, and the antigen-antibody reaction occurs, which ultimately leads to the destruction of the red blood cells by lysis. Therefore, red blood cell agglutination is caused by antigen-antibody reaction, which ultimately causes the lysis and destruction of red blood cells, which is why the principle of transfusion of blood of the same blood type is used in clinical practice.