The most important blood groups in transfusion are the ABO blood group system and the RhD blood group system.
Blood groups are determined by a protein (antigen) on the surface of the red cell. So, the ABO system has A and B antigens and the RhD system has the D antigen.
In all, there are 30 major blood group systems. This means a person may be A RhD positive, and at the same time Kell (Kell system) positive, M and N (MNS system) positive and Lea and Leb (Lewis system) positive.
The ABO blood group system
If you have blood group A then you have got the A antigen on your red cells.
Blood group B means you have the B antigen, while group O has neither, and group AB has both A and B antigens.
The ABO system has associated anti-A and anti-B antibodies, antibodies being the body's natural defence against foreign antigens. These antibodies are found in the plasma.
Blood group A has the A antigen. This group recognises the B antigen as foreign and can make anti-B antibodies.
Similarly, blood group B has the B antigen and therefore recognises the A antigen as foreign and can make anti-A antibodies.
Group AB has both the A antigen and the B antigen so this group makes no antibodies.
Group O has neither A nor B antigen so this group can be given safely to any other group. This is why Group O donors are known as "universal donors". Group O can make both anti-A and anti-B antibodies if exposed to these antigens.
Giving someone blood from the wrong ABO group could be life-threatening.
For instance, the anti-A antibodies in group B attack group A cells and vice versa. This is why group A blood must never be given to a group B person.
The RhD system
Another important blood group system in transfusion is the RhD system.
85% of people have the D antigen on their red blood cells and are RhD positive.
The remaining 15% lack the D antigen and are RhD negative.
Your blood group is defined by your ABO group together with your RhD group. For instance, someone who is group A and RhD negative is known as A negative.
The chart below explains the national distribution of blood groups. Click on a blood type for more information.
|ABO Blood Group||Rh(D) Type||Percentage of Population with this Group|