Blood Group Basics

The most important blood groups in transfusion are the ABO blood group system and the group D of the Rh system.

Blood groups or antigens are determined by either sugars or proteins on the surface of the red blood cell. The ABO system has A and B antigens and the Rh system has many antigens but D is the most important.

There are 35 blood group systems. This means a person who is AD positive may also be K positive (Kell system), M and N positive (MNS system) and Fya positive but Fyb negative (Duffy system) and so on.

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.

Group O has neither A nor B antigens on the surface of their red cells so red cells of this group can be given safely to any other group. This is why group O donors are known as "universal red cell donors". Group O makes both anti-A and anti-B antibodies.

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 and are unusual in that they are ‘naturally occuring’ so they don’t need to be stimulated – such as by having a transfusion or during pregnancy. This means that blood from someone with blood group A contains anti-B antibodies.

Similarly blood from someone with blood group B contains anti-A antibodies and those with group O contain both anti-A and anti-B whilst those with group AB have neither anti-A nor anti-B.

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

For instance, the anti-A antibodies in a recipient with group B blood group will attack the group A cells if this transfused to them. This is why group A blood must never be given to a group B person.

The Rh system

Another important blood group system in transfusion is the Rh system. The most important antigen of the Rh system is D.

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

83% of our donors have the D antigen on their red blood cells and are D positive.

The remaining 17% lack the D antigen and are D negative. (Source – NHS Blood and Transplant; Active Donor Base 2013/14).

The Rh system is slightly more complicated as discussed below.

The Rh blood group system has two Rh genes (D and CE).

CE produces four combinations; ce, Ce, cE or CE

The most frequently occurring phenotypes of Rh CE and Rh D are Dce, dce, DCe, dCe, DcE, dcE, DCE and dCE.

Sometimes we will communicate specifically with groups of donors who have specific phenotypes such as those who have the Dce or the ‘Ro’ subtype or phenotype. While Ro blood is rare amongst White European people, it is much more common amongst Black African and African Caribbean people.

The Ro phenotype is over 10 times as common in individuals from Black backgrounds compared to individuals from White backgrounds and is very common in patients with sickle cell disease.

This fact that Ro donors are much more commonly found in the Black population is one of the reasons why we are asking many more Black Asian and Minority Ethnic donors to donate blood.

Ro blood is needed for patients who also have Ro blood. Often, these patients are those who require ongoing blood transfusions - many of our sickle cell patients.

The Distribution of Blood Groups

The chart below explains the distribution of blood groups within our donor base and the issue of blood to hospitals. 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. Click on a blood type for more information.

ABO Blood Group % of donor population with this group % of blood issued to hospitals
A + 33% 31%
A - 7% 8%
B + 9% 8%
B - 2% 2%
O + 38% 36%
O - 8% 12%
AB + 3% 2%
AB - 1% 1%

Data accurate at 31 March 2014. Data accurate to the nearest percentage.
(Figures rounded up to the nearest whole number)

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Did you know?

Each blood donation can help as many as 3 people

100 donations equates to
47 litres of blood

We collect around 1,700,000 blood donations each year

B- Blood is rare

Only 2% of our donors are B-

9% of donors live in
Greater London

10% of donors are donating for the first time

Another fact