UNIT II

 ABO Blood Group System

• 2.1 Antigens and antibodies involved

• 2.2 Principle and procedure of ABO blood grouping

• 2.3 The Rh Blood Group System, Antigen, and antibody involved

• 2.4 Principle and procedure of Rh grouping

Author: Dr Pramila Singh.

ABO Blood Group System

ABO blood group system is a classification system that classifies human blood into four groups. This classifies human blood based on specific antigens present or absent in the red blood cells. It is the most accepted and widely used blood group system in blood transfusion.

ABO system divides blood group into four main groups. These are blood group-A, Blood group-B, Blood group-AB, and Blood group-O. This classification is based on the presence and absence of two antigens on the red blood cell surface and two antibodies. These are antigen-A and antigen-B. And Antibody-a and antibody-b in blood plasma.

1.  Blood group A: The surface of Red blood cells has antigen-A and blood plasma has antibody-b.

2. Blood group B: The surface of Red blood cells has antigen-B and blood plasma has antibody-a.

3. Blood group AB: The surface of Red blood cells has antigen-A and antigen-B, and blood plasma has no antibody.

4. Blood group O: The surface of Red blood cells has no antigen and blood plasma has both antibody-a and antibody-b.

2.1 Antigens and antibodies involved

Two antigens and two antibodies are involved to determine the blood group under the ABO blood group system.

A. Antigens (Agglutinogen)

1. Antigen-A (Agglutinogen-A): It is a specific carbohydrate present on the surface of red blood cells under blood group A.

2. Antigen-B (Agglutinogen-B): It is a specific carbohydrate present on the surface of red blood cells of individuals under blood group B

B. Antibodies (Agglutinins)

1. Antibody-a (Anti-A Antibody): These antibodies are present in the blood plasma of individuals belonging to blood group B and blood group O. Anti-A Antibodies are present in blood group B and blood group O naturally. They are also produced by the human immune system after entry of antigen A in blood group B and blood group O.

2. Antibody-b (Anti-B Antibody): These antibodies are present in the blood plasma of individuals belonging to blood group A and blood group O. Anti-B Antibodies are present in blood group A and blood group O naturally. They are also produced by the human immune system after entry of antigen B in blood group A and blood group O.

3. Anti-A and Anti-B antibodies: These antibodies are not present in blood plasma and belong to blood group AB.

The interaction between antigens and antibodies is called antigen-antibody reaction. This interaction decides blood compatibility. Incompatibility in blood transfusion develops if there is the mixing of antigen-A and anti-A antibodies (Antibody-a). Similarly, blood incompatibility in blood transfusion develops if there is the mixing of antigen-B and anti-B antibodies (Antibody-b). This interaction causes agglutination of red blood cells (Clumping of red blood cells). It is dangerous and life-threatening.

Based on antigens and antibodies present in the blood, the following guidelines are followed in blood transfusion

• Blood group A: Blood group A can receive blood from donors belonging to blood group A and blood group O. Blood group A cannot receive blood from donors belonging to blood group B and blood group A.

  Explanation: Blood group B has an Anti-A antibody. Anti-A antibody of donor blood group B will interact with antigen-A of recipient blood group A. This interaction will cause red blood cell agglutination.

• Blood Group B: Blood Group B can receive blood from donors belonging to Blood Group B and Blood Group O. Blood Group B cannot receive blood from donors belonging to blood group A and blood group A.

  Explanation: Blood group A has an Anti-B antibody. Anti-B antibody of donor blood group-A will interact with antigen-B of recipient blood group-B. This interaction will cause red blood cell agglutination.

• Blood group-AB: Blood group AB can receive blood from blood group AB, Blood group A, Blood group B, and blood group O. Thus blood group-AB is a universal recipient. However, this policy is practiced only in war situations or emergency conditions. In routine blood transfusion, only blood group AB is given to patients of blood group AB.

  Explanation: Blood group AB has antigen A and antigen B on the surface of red blood cells. It does not have either anti-A antibody or anti-B antibody in its plasma. Thus it is considered a universal recipient.

• Blood group-O: Blood group-O has both Anti-A antibody and Anti-B antibody in its plasma. Thus it can receive blood only from blood group blood. It is considered a universal donor. However, this policy is practiced only in war situations or emergency conditions. In routine blood transfusion, only blood group O is given to patients belonging to blood group O.

2.3 Principle and procedure of ABO blood grouping

Principle: ABO blood grouping system classification of human blood based upon the presence or absence of antigen (agglutinogen) on the surface of red blood cells. These antigens are antigen-A and antigen B. ABO blood grouping system follows the following principles

A. Antigen

1. Antigen-A: Individuals under blood group A have antigen-A on the surface of red blood cells.

2. Antigen-B: Individuals under blood group B have antigen-B on the surface of red blood cells.

3. Antigen-AB: Individual under blood group AB has both antigen-A and antigen-B on the surface of red blood cells.

4. Antigen-O: Individuals under blood group AB have neither antigen-A nor antigen-B on the surface of red blood cells.

B. Antibody

1. Anti-A antibody: Individuals under blood group B and blood group O have antibodies against antigen-A in their blood plasma.

2. Anti-B antibody: Individuals under blood group B and blood group O have antibodies against antigen A in their blood plasma.

3. Anti-AB antibody: Individuals under blood group O have antibodies against both antigen-A and antigen-B in their blood plasma.

The following two methods are used to determine the ABO blood group of an individual. These are the slide method and tube method. Both methods act on the same principle. Both methods use antiserums as a reagent. These antiserums are

1. Anti-A Antiserum: Individuals under blood group B have Anti-A antibody (agglutinin-a) in their blood plasma. Anti-A Antiserum is collected from blood group B. The addition of Anti-A antiserum on a slide or test tube containing blood shows an agglutination reaction. This confirms blood is blood group A.

    Explanation: Blood group A has antigen A on the red blood cell surface. Its plasma has an anti-B antibody but no anti-A antibody. The addition of Anti-A Antiserum will interact with antigen-A present on the red blood surface. This interaction causes agglutination.

2. Anti-B Antiserum: Individuals under blood group A have Anti-B antibody (agglutinin-b). Anti-B Antiserum is collected from blood group A. The addition of Anti-B antiserum on a slide or test tube containing blood shows an agglutination reaction. This confirms blood is blood group B. 

   Explanation: Blood group B has antigen B on the red blood cell surface. Its plasma has an anti-A antibody but no anti-B antibody. The addition of Anti-B Antiserum will interact with antigen-B present on the red blood surface. This interaction causes agglutination.

3. Anti-AB Antiserum: Blood group B has both antigen-A and antigen-B. Anti-AB Antiserum is collected from blood group O. The addition of anti-AB antiserum on a slide or test tube containing blood shows an agglutination reaction. This confirms blood is blood group AB. If there is no agglutination then it confirms blood group-O. Explanation: Blood group AB has antigen A and antigen B on the red blood cell surface. Its plasma has neither anti-A antibody nor anti-B antibody. The addition of Anti-AB Antiserum will interact with antigen-A and antigen-B present on the red blood cell surface of blood group-AB. This interaction causes agglutination.

Blood group O has neither antigen-A nor antigen-B on the red blood cell surface. Its plasma has both anti-A antibody and anti-B antibody. There will be no agglutination upon the addition of Anti-AB Antiserum because neither antigen-A nor antigen-B are present on the red blood cell surface.

Procedure:

1. Collection of blood samples: Collect blood samples by using a sterile needle and syringe or by finger prick method. Place it into a test tube or well of slide.

2. Addition of reagent: Place a drop of Anti-A Antiserum into a test tube or well of slide. Place a drop of Anti-B Antiserum into another test tube or well of the slide. Keep the third test tube or well of the slide containing blood as a control sample.

3. Mix and observe: Mix blood and reagents in a test tube or slide. Observe for agglutination of red blood cells.

4. Conclusion:

• · If agglutination occurs in a test tube or well with Anti-A Antiserum, indicates blood group –A.

• · If agglutination occurs in a test tube or well with Anti-B Antiserum, indicates blood group –B.

• · If agglutination occurs in both test tubes or well with Anti-A Antiserum and Anti-B Antiserum, indicates blood group –AB.

• · If agglutination does not occur in a test tube or well with Anti-A Antiserum and Anti-B Antiserum, indicates blood group –O.

Author: Dr Pramila Singh