Blood type O can only receive blood from patients with type O. The red blood cells of type O patients do not have A and B antigens, and the serum plasma contains anti-A and anti-B antibodies. Other blood types, such as A, B or AB, have A antigen, B antigen, or both A antigen and B antigen on the surface of red blood cells, and red blood cells of other blood types cannot be transfused to O patients, otherwise they will cause serious hemolytic reactions, so O patients can only receive O blood and cannot receive red blood cells of any other blood types. Plasma type O patients can receive AB plasma because AB plasma has no anti-A and anti-B antibodies, and red blood cells of type O patients also have no A and B antigens inside, so they will not cause transfusion reactions. However, non-homotypic transfusions are only given under special circumstances, sometimes in emergency situations, when the patient’s blood type is unknown, and only in the case of life-saving, non-homotypic blood is used, basically homotypic transfusions should be followed, and the transfusion department in the hospital will strictly follow the implementation of homotypic transfusions.