Blood group basics

About blood 

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.

78% of our donor base have the D antigen on their red blood cells and are RhD positive.

The remaining 21% (allowing for some rounding down of figures) 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 distribution of blood groups within our donor base and the distribution of blood to hospitals. Click on a blood type for more information.

It’s important that we collect enough of the right type of blood in the right quantities to meet the needs of hospitals and patients across England and North Wales. The following table shows blood group data relating to our active donor base and the blood we issue to hospitals.

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