The basis for the ABO and Rh Blood Groupings

There are more than 100 types of genetically determined antigens that have been detected on the surface of the red blood cells that appear in a characteristic pattern that enables scientists and health care professionals to identify a person’s blood as belonging to one or more blood groups.

There are currently 14 known blood group systems, and each is characterized by the presence or absence of specific antigens on the surface of the red blood cells plasma membrane.

The most commonly known and used are;

  • ABO Blood Grouping System
  • Rh Blood Grouping System

ABO Blood Grouping System

  • It is based on two antigens that are symbolized as A and B.
  • Individuals whose erythrocytes manufacture only antigen A are said to be of blood type A and those whose erythrocytes manufacture antigen B are said to be of blood group B.
  • Those whose red blood cells manufacture both antigen A and B are said to be blood group AB.
  • Those whose red blood cells manufactures neither A nor B antigen are said to belong to blood group O
  • Blood plasma contains antibodies/immunoglobulin that react with the A and B antigens if they are mixed.
  • These antibodies include; the anti-A antibody that reacts with antigen A and the anti-B antibody that reacts with antigen b

One lacks antibodies that react with the antigens of their own red blood cells but instead have antibodies for any of the antigens that their red blood cells lack. I.e.  If one is of blood type A he/she possesses A antigens on the plasma membrane of his/her red blood cells and also have the anti-B antibodies in his/her blood plasma

Rh Blood Grouping System

  • It is called rhesus antigen/rhesus factor because it was first found in the blood of a rhesus monkey.
  • It is also called the D antigen
  • Individuals whose red blood cells have the rhesus antigens/D antigen are designated Rh+ and those whose red blood cells lack the rhesus antigen are designated Rh-.

Importance of Blood Grouping Knowledge

  • The knowledge of blood group is important especially during transfusion that is normally given to treat low blood volume, anaemia, low platelet count.
  • In an incompatible blood transfusion antibody in the recipient’s plasma binds to the antigens on the red blood cells of the donor and cause agglutination of the red blood cells.
  • Agglutination is an antigen-antibody response in which the red blood cells become cross-linked to one another to form an antigen-antibody complex that activate complement proteins called globulins that makes the plasma membrane of the donated red blood cells leaky causing haemolysis of the erythrocytes to release the globulin into the bloodstream.
  • The liberated haemoglobin can cause kidney damage and jaundice.

Although rare, it is possible for viruses that can cause AIDS and hepatitis B and C to be transmitted through transfusion of the contaminated blood products.

Written by Alphonse Oyugi


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