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Blood Group ABO/Rh

The blood group is one of the classification systems of human blood. In the erythrocytes or red blood cells there are adhered substances, the antigens, that define these blood groups and that are responsible for a donor and a recipient in a blood transfusion. In total there are more than 300 antigens that may or may not be on the surface of red blood cells and that are those that mark blood groups. There are more than 30 blood type classification groups, but the two most important are the ABO group and the Rh group because they affect the vast majority of the world’s population.
People in group A have antigen A. People in group B have antigen B. People in group AB have both antigens and people in group O have neither. This is the ABO classification.

Likewise, in the Rh classification, Rh + people present the Rh antigen while Rh- do not.

These antigens found on the surface of red blood cells (A and B antigens for the ABO classification system; Rh antigen for the Rh classification system) react when they come into contact with blood that is of a different type and does not have the same antigens on the surface of the red blood cells. When this happens, the unsupported blood recipient makes antibodies against these different antigens of the donor. The presence or not of each type of antigen (For the ABO system: A, B, AB-presenting both antigens, O-presenting neither antigen A nor antigen B; For the Rh system: Rh + individual presents the Rh antigen, Rh – individual does not present the Rh antigen) is the factor that determines who can give blood to whom.


  • ABO
  • RHD