10 Most important things to know ABO blood group system

One of the popular categorization of blood is the ABO blood group system.

Before we can understand the peculiarities in the different blood groups, we will have to understand the basics of the system.

This classification is based on immunological response between antigen and antibody as inherited by the red blood cells. These antibodies can also be referred to as agglutinogens.

This is because they have the capacity to cause agglutination (lumping of blood cells) of the red blood cells. Blood showing type A antigen on the surface of their cells naturally have the ability to attack type B red blood cell, resulting to Agglutination.

Now this means that if blood from type B red blood cells is transfused into a Type A carrier, the transfused blood will be destroyed by the recipients Type A antibodies. Likewise when the scenario is repeated anti-clock-wisely.

The reason why this happens is because for every antigen present on the surface of the RBC’s, their corresponding agglutinin must be absent in their serum.

To explain this further, if antigen A is found on the surface of an RBC, the agglutinin for A must not be found in the serum of the cell or If a particular antigen is absent in the RBCs surface, the corresponding agglutinin must be present in the serum.

This explains the reason why the blood type A will not destroy transfused blood type A, rather it will destroy any other one apart from O.

The ABO blood group system (antigens) is well developed well before birth and remains throughout individual’s life existence.

There is no doubt that the ABO blood group system is acquired passively from mothers to children before childbirth. The children actively by the age of three months should start generating their own antigens.

ABO blood group system is categorized based on the presence or absence of antigen A and antigen B on the RBC surface.  ABO blood group system is divided into four groups:

  • ‘A’ group
  • ‘B’ group
  • ‘AB’ group
  • ‘O’ group

Blood having antigen A belongs to group ‘A’. This blood has B-antibody inside the serum. Blood with antigen B on the cellular surface and A –antibody inside its serum belongs to ‘B’ group.

If both the antigens A and B are present on the surface of the cell, the blood group is referred to as ‘AB’ group and serum of this group does not contain any antibody ( agglutinogen). If both Antigens A and B are absent, the blood group is called group ‘O’  and both A and B antibodies(agglutinogens) are present inside the serum of the RBC.

Importance of ABO blood group system

When blood is been transfused, only compatible blood must be given. The ‘donor’ is the one who gives blood while the ‘recipient’ is the one who receives the blood been transfused.

Before transfusion of blood is made, special considerations concerning the antigen of the donor and the antibody of the recipient are to be factored. In most cases, the antibody of the donor and antigen of the recipient are ignored leading to preventable death.

RBC of ‘O’ group has no antigen on their surface and so agglutination does not occur with any other group of blood. With this, blood group   ‘O’ can be given to any other blood group persons and the people with this blood group are referred to as ‘universal donors’.

The serum of AB group blood has no antibody. Therefore it does not cause agglutination of RBC from any other group of blood in the case of blood transfusion. People with AB group can receive blood from any other blood group persons.  Therefore, people with this blood group are mostly referred to as ‘universal recipients’.

abo blood group system by idealmedhealth
abo blood group system

what happens when the wrong red blood cell is transfused to a recipient?


A hemolytic transfusion reaction occurs when the red blood cells given during transfusion are destroyed by the recipient’s immune system.

They are the adverse reactions in the body, which occur due to transfusion error that involves transfusion of mismatched blood.

These reactions may be mild causing only fever and skin disorder characterized by itching or may even slip to severity of case leading to renal failure, shock and eventually to death.

If there is a mismatch in transfusion, reactions occur between donor’s RBC and recipient’s serum. So, if the donor’s serum contains agglutinins (antibody) against recipient’s RBC, agglutination will not occur. This is because the donor’s antibodies are diluted in the recipient’s blood.

However, if recipient ‘serum contains agglutinins against donor’s RBCs, the immune system launches a response against the new blood cells.

Therefore, donor RBCs are agglutinated (blood cells are clumped together) resulting in transfusion reactions.

We want to believe that, to an extent we have done great justice to this topic; the ABO blood group system.

With this knowledge, I believe we have come to note how important it is for us to know the group to which our antigen is classified. This will enable swift and safer decision making incase of emergencies that will demand blood transfusion.

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