Blood groups
Antigens and antibodies
Your blood group is identified by antigens and antibodies in the blood. Antibodies are part of your body's natural defences against invading substances such as germs.
Antigens are protein molecules found on the surface of red blood cells. Antibodies are proteins found in plasma. Antibodies recognise anything foreign in your body and alert your immune system to destroy it.
Medically Reviewed by a doctor on 21 Dec 2018
Introduction
There are four different blood types, known as blood groups. The four main blood groups are A, B, AB and O.
What is blood?
Your body carries aroundfourto six litres (7to 10.5 pints) of blood. Blood is made up of red blood cells, white blood cells and platelets in a liquid called plasma. Plasma is about 90% water, but als
Antigens and antibodies
Your blood group is identified by antigens and antibodies in the blood. Antibodies are part of your body's natural defences against invading substances such as germs. Antigens are protein molecules f
The ABO system
There are four main blood groups defined by the ABO system: blood group A has A antigens on the red blood cells with anti-B antibodies in the plasma blood group B has B antigens with anti-A ant
The Rh system
Red blood cells sometimes have another antigen, a protein known as the RhD antigen. If this is present, your blood group is RhD positive. If it's absent, your blood group is RhD negative. This means y
Blood group test
To work out your blood group, your red cells are mixed with different antibody solutions. If, for example, the solution contains anti-B antibodies and you have B antigens on your cells (you are blood
Pregnancy
Pregnant women are always given a blood group test. This is because if the mother is RhD negative but the child has inherited RhD-positive blood from the father, it could cause complications if left u
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