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Know your blood group

ABO blood groups

The most important blood groups in transfusion are the ABO blood group system. The four main blood groups in the ABO system are:


Which group you belong to is determined by the genes inherited from both parents.

The surface of a red blood cell is coated with a combination of sugars and proteins called antigens. Depending on your combination, you will have A antigens, B antigens, no antigens or both A and B antigens. It is the presence of the A and B antigens and corresponding antibodies in the clear part of blood called plasma, that determines an individual’s blood group.

Antibodies are the body’s natural defence system. They recognise any ‘foreign’ antigens and inform your immune system to destroy them. The antibodies found in plasma are unusual in that they are ‘naturally occurring’ meaning they don’t need a stimulus such as a transfusion or pregnancy to be created. 


Antigens on
red cell

in plasma



anti-A & anti-B








A and B



Giving someone blood from the wrong ABO group can be life-threatening.

If a patient with blood group B received a transfusion from a donor with blood group A, their anti-A antibodies would attack the group A cells transfused to them. This is why group A blood must never be given to a group B person and vice versa.

Blood group O has neither A nor B antigens on the surface of its red cells so the antibodies in groups A, B and AB do not identify it as foreign when transfused. This is why blood group O is often referred to as the ‘universal red cell'.

Group AB has no anti-A or anti-B antibodies so does not identify the antigens on the surface of blood groups A, B or O as foreign. This means that patients with group AB blood can receive donations from groups A, B and O.

The Rhesus system

Another important blood group system in transfusion is the Rhesus system.

There are 5 main Rhesus (Rh) antigens on red cells – C, c, D, E, e.

The most important of these is the Rh D group. The D antigen on the red cell is what gives you the positive (+) or the negative (-) after the letter A, B, AB or O.

Find out more about the Rh system here.

What blood do we need?

The chart below shows the distribution of blood groups among our donors. 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.

  ABO blood group   

  % of donor population
with this group 

A +


A -


B +


B -


O +


O -


AB +


AB -


Data accurate at 30 June 2017.  
(Percentage figures have been rounded to the nearest whole number)