It has always been said that blood type O is the universal blood type and can be lost to any blood type, so what is the truth? First, let’s look at some general knowledge about blood types. The human ABO blood type system is controlled by three alleles, A, B and O, and is passed on according to the law of inheritance, that is, in the relative loci of a pair of autosomes, the three alleles, A, B and O, can be rotated to occupy, therefore, there are six gene combinations: AA, AO, BB, BO, AB and OO. This gene combination is called genotype. Among the genes, A and B are dominant factors and O is a recessive factor, so there is a situation where the genes of the blood type are not necessarily the same as the expression of the blood type. For example, people with AA and AO genes have the expression form of blood type A; people with BB and BO genes have the expression form of blood type B; only people with OO genes have the expression form of blood type O. Accordingly, it is not difficult to infer the possible and impossible blood types of children from the blood types of their parents. The ABO blood group system is the most commonly mentioned blood group system, in which the distinction between the four types A, B, AB, and 0 is based on the distribution of antigens on the surface of red blood cells, i.e., those with A antigens on red blood cells are type A, those with B antigens are type B. When both A and B antigens are present, the blood type is AB, while those without both A and B antigens are type O. If we look at red blood cells alone, type O, which has neither A nor B antigens, is indeed very “safe”, and perhaps this is why it is mistakenly regarded as the “universal blood”. However, it is important to know that in addition to red blood cells, there are also white blood cells, platelets, plasma and other substances. Although there are no A and B antigens on type O red blood cells, the plasma contains anti-A, anti-B and anti-AB antibodies, and if these antibodies enter the body of non-type O patients, an antigen-antibody reaction will occur, resulting in immune hemolytic transfusion adverse reactions, which is very dangerous! People with different blood types cannot transfuse each other. The reason why type O blood is called “universal blood” is because type O red blood cells lack A and B antigens, therefore, this type O red blood cells can be transfused to people with type A, B and AB. When it is difficult to identify the ABO blood type of the recipient, as well as when there is a shortage or lack of homotypic blood in a life-saving emergency, a small amount of type O washed red blood cells can be imported to meet the urgent need. However, O plasma contains anti-A and anti-B antibodies, which can sensitize or agglutinate A, B and AB red blood cells, shortening their life span or destroying them immediately, which is a contraindication to blood transfusion. Therefore, the medical profession refers to O whole blood as “dangerous universal blood”. People mistakenly think that O blood is the “universal blood”, but in fact, the word “dangerous” is ignored. As the amount of allogeneic transfusion increases, this contraindication to transfusion will gradually worsen, and in severe cases, the destruction of the recipient’s red blood cells will lead to hemolytic transfusion reactions. It is worth mentioning that although conventional O blood is not really a “universal blood”, it does have more “skills” than the other three blood types. If O red blood cells are “washed” to remove most of the white blood cells, platelets, plasma and other substances to make “washed red blood cells”, they can be safely transfused to people with A, B, AB and their various subtypes, but they still need to be However, it is still necessary to perform a blood test before transfusion. The distribution of Rh negativity varies greatly by race, with a higher percentage of Caucasians. The proportion of Han Chinese is very small, only three to five thousandths, which is a rare blood type. The belief that O blood type is the universal blood is a statement from the past when science was not developed, but with the progress of science, this statement is no longer valid. Therefore, O blood type is not a universal blood donor, and cross-matching test must be used for blood transfusion, and the same type must be transfused. In places with better medical conditions, component transfusions should be vigorously promoted and allotypic transfusions should not be used.