General Science Bullet – All you need to know about Blood groups – Capsule 2

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As transfusion of wrong blood groups leads to severe complications and even sudden death, it is necessary for us to know the reason behind effects. In this article, we will understand the reason for incompatibility between various blood groups.

Key terms

1. Antigen: It is a substance, which upon entering the body stimulates the production of antibodies as a response from the immune system. However, if the antigen is produced in the body itself (self-antigen), it does not trigger such a response.

2. Antibody: Also known as immunoglobulins, antibodies are proteins produced by the immune system to destroy/neutralise any antigen that enters the body. The action of an antibody is specific – it reacts to only those antigens that are specific to its structure, thus causing its disruption and clot formation.

3. Blood serum: It is a component of blood that is yellowish in colour and carries electrolytes, antibodies, hormones and other exogenous substances.

4. Coagulation: Also known as clotting, it is the process in which liquid is converted to a gel-like substance. When an antigen reacts with its specific antibody, it results in formation of a clot.

Why various blood groups are incompatible?

The main reason for incompatibility between different blood groups is due to the structural differences between them, though their basic structure remains the same. On the surface of RBCs, antigen-H is present, which is common to all the blood groups. This antigen is responsible for the formation of other antigens. However, a rare deficiency of antigen-H is found in few people termed as Bombay phenotype/ Bombay blood group h/h also known as  Oh (first discovered in a few people in Bombay, hence the name).

Blood group A: People with blood group A have antigen-A present on the surface on their RBCs. Also, they have antibodies for antigen-B i.e anti-B antibody present in the blood serum.

Blood group B: People with blood group B have antigen-B present on the surface on their RBCs. Also, they have antibodies for antigen-A i.e anti-A antibody present in the blood serum.

Blood group AB: People with this blood group have both antigens (antigen-A and antigen-B) present on the surface of their RBCs. No antibodies for antigen-A and antigen-B are found in the blood serum.

Blood group O: People with this blood group have no antigens present. Also, they have antibodies for both antigen-A and antigen-B i.e anti-A antibody and anti-B antibody present in the blood serum.

This means if a patient with blood group A receives blood of B type, the anti-B antibody present naturally in his blood will react with the foreign antigens and destroy it resulting in disruption of the RBCs. This phenomenon is known as Acute Hemolytic Transfusion Reaction (AHTR). It occurs within 24 hours of the transfusion and can be life threatening if not cured.

On the other hand, if the patient has blood group O, a similar coagulation will occur if he is given blood from either A/ B groups. Therefore, it is of vital importance to examine the patient’s blood before any transfusion.

Link to All you need to know about blood groups – Capsule 1:…

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