Blood Group Serology


The ABO system is the most important blood group system in blood transfusion and organ transplanta- tion because of two unique features.

  1. Strongly reactive antibodies are present in the serum of individuals who lack the correspond- ing antigens.
  2. A and B antigens are present on many tissue cells in addition to the red cells.
    The ABO system consists of four blood groups or phenotypes: A, B, AB and O. The two antigen, A and B are responsible for these four groups. If A antigen is present on the red cell, the individual is said to belong to group A, those having B antigen are group B persons. Group AB individuals have both A and B antigens while group persons have neither A nor B antigen on their red cells. Three allelic genes, A, B and O, can be inherited in the ABO system. The following combinations of alleles is possible: AA, AO, AB, BB, BO, oO; resulting in A, A, AB, B, B, and O group individuals respectively. This is so because A and B genes are dominant and O gene is recessive.
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Group O individuals have an antigen called H antigene on the surface of their red cells which is a precursor of A and B antigen.

Test for Blood group
1. Blood sample
2. ABO grouping Antisera: anti-A, anti-B, and anti-D or anti-AB.

1. A drop of sample (blood) was placed on 3 spots of a clean tile.
2. Anti-A was dropped on the first spot of the tile, then anti-B on the second and anti-D on third respectively.

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  1. Mix both sample and serum in each spot using separate applicator sticks.
  2. Rock the tile gently and observe for agglutinations.


For Positive blood groups the O Gene always react because it’s a recessive Gene!

For negative blood groups the O Gene doesn’t reacts.

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