Appendix 02. Four major groups

 

Four major groups of A, B, AB, and O are defined by the presence or absence of 2 antigens (A and B) on RBCs, and of the antibodies against these antigens in sera. Blood group A individuals have A antigens on RBCs and anti-B antibodies in serum. Similarly, blood group B individuals have B antigens on RBCs and anti-A antibodies in serum. Blood group AB individuals have both A and B antigens on RBCs and neither anti-A nor anti-B antibodies in serum. On the contrary, blood group O individuals have neither A antigens nor B antigens, but possess both anti-A and anti-B antibodies in serum. The observed rule that individuals have the antibodies against A or B antigens if they do not express A or B antigens on RBCs, respectively, has been named the Landsteiner’s Law. The presence or absence of A or B antigens can be detected by the RBC agglutination reaction, using the anti-A or anti-B reagents (the forward test). The presence or absence of anti-A or anti-B antibodies in serum can be detected by the RBC agglutination reaction, using the reference A1 and B RBCs (the reverse test).  These tests are routinely used to determine ABO blood type at any hospital.