Why is type O blood the Universal donor?
Blood type represents four different classes of blood which are classified depending on the type of antigenic substances that are available on the blood cell membrane. The antigens may be of proteins, carbohydrates, glyco-lipids or glyco-proteins. These antigens may be present on the cells of other tissues too. The antigens that are translated from the alleles or same kind of genes are grouped into one blood type. This classification or grouping of blood depending on the source of the antigens is called as blood grouping system. The blood types or groups will be brought from the parents and inheritance of blood group will occur. The international society of blood transfusion was found to have identified about 30 blood group systems.
The most important blood group system found in human blood was ABO system. Blood group O’ is also called as Zero blood group. This group is called as zero because the red blood cells in this grouping system do not have A antigen or B antigen on their surfaces. The serum of the blood consists of immunoglobulin M antibodies for A and B antigens. Blood group O can be given to any person having any blood type as it does not contain antigens for A and B for agglutination to occur with either of the antibodies in the other blood types. Hence, O group is otherwise called as universal donor. But, as it consists of antibodies for A and B antigens, the person with O blood group can receive only O group blood and not any other. Since, the O group does not have antigens to react with the antibodies available in the recipient O group; O group recipients can get only O group blood.
Blood group O is called as universal donor as it can be donated to any person having either A or B or AB or O blood groups. This ability of it is due to the absence of A and B antigens on the surface of blood cells.