The ABO Blood Group System

The ABO blood group system is used to categorise human blood. ABO antigens (which can be attacked by disease-fighting antibodies) appear on the surface of red blood cells.

Type A blood has type A antigens, type B blood has type B antigens, type AB blood has both types of antigens and type O has neither. Also, type A blood has anti-B antibodies and visa versa, type AB has neither types of antibodies and type O has both anti-A and anti-B antibodies.

This means that type A blood for example, only has type A antigens and has anti-B antibodies. So if type A blood is exposed to B antigens (i.e. if the patient receives type B blood) it will want to destroy them with its anti-B antibodies, resulting in agglutination (clumping of cells). So if a donor provides type B blood to a type A recipient, a transfusion reaction would occur because there will be a clumping of the natural anti-B antibodies of the recipient onto the foreign type B antigens from the donor.

People with type O blood have been called universal donors, because as previously mentioned they have no antigens for recipient’s antibodies to react to. For example, if type O blood were given to a type A recipient, it will not react with the anti-B antibodies that the type A blood has.

ABO blood grouping maybe a little bit difficult to get your head around. So it’s probably a good idea to read this post twice. If you still don’t understand, please leave a comment and I’d be glad to help.