There is no such thing as a universal blood type. In the past, in clinical practice, blood type O was the universal blood, because there was no A antigen and no B antigen on the red cell membrane of blood type O. When transfusing blood to a patient, the donor’s red cell membrane would not have an agglutination reaction with the antibodies in the recipient’s serum due to the absence of the A antigen and the B antigen, so, in the past, blood type O was called the universal blood. However, in reality, transfusion of type O blood to a person with non-type O blood may produce a febrile reaction or even a very serious hemolytic reaction. This is because the anti-A and anti-B antibodies in people with blood type A and B are IgM in nature. They are easily neutralized by substances of the corresponding blood type, while anti-A and anti-B antibodies in blood type O are IgG in nature and are not easily neutralized, resulting in a transfusion reaction. The current principle of blood transfusion is to transfuse blood of the same type, and a cross-matching test must be done before transfusion, only blood of the same type without agglutination reaction can be imported, and only when there is no blood of the same type in an emergency situation can O-type blood be imported in small quantities. Therefore, there is no such thing as universal blood.