The ABO system, the first known blood grouping system, was discovered in 1901. Its name derives from the three groups that are identified: those of antigen A, antigen B, and O without antigens.
How do we get our blood type?
Blood type is inherited in the genes, just as it is with all other physical characteristics.
The ABO group is the most important blood group system and includes blood groups A, B, O and AB. The next most important system is the Rh, according to which we can be Rh positive or Rh negative.
In total there are eight basic blood groups: A, B, AB and O, each of which can be Rh positive or Rh negative.
The importance of the ABO group lies in its great impact on the compatibility of blood used for transfusion. If we are transfused blood that is incompatible with our blood group, we can have such an intense rejection that it can cause death.
How common are the blood types?
The number of people who have one blood type or another varies according to race. For example, blood group B is more common in Asia, while group O is more common among Europeans.
There are two copies or alleles in each gene. Combinations of these copies (we inherit one gene from the mother and one from the father) give rise to the different ABO types. It should be noted that the A and B antigens are dominant, while the O antigen is recessive. For example, a person who inherits an A gene and an O gene will have blood group A.
What is the compatibility between blood groups?
The great importance of the ABO group lies in the need to know how and against what our antibodies act. Each person creates antibodies from the first months of life against the antigens he/she does not have. If I am group A, I have antigen A and I do not have antigen B. I will naturally have antibodies that destroy red blood cells with B antigen. Therefore, the presence of the antibodies that we have created will end up determining the compatibility of our blood.
People of group O have neither A nor B antigen, so they will have made antibodies that act against both A and B. Therefore, only O blood, which is free of both A and B antigens, can be transfused to group O persons. It is for this reason that type O is considered to be a universal donor, especially if it is Rh negative. In this case the blood does not carry A, B or D antigen (which is the main Rh antigen).
People with group O- are universal donors, although they can only receive blood from their own group. On the other hand, people with group AB+ are universal recipients. This means that they can receive blood from any group, but their blood is only usable for people of the same group.
For more information, consult your hematologist.