ABO blood groups

ABO blood groups is the system by which human blood is classified, based on proteins occurring on red blood cells. The two main ways to classify blood groups are the ABO system and the Rh system. Together, they make up the eight main blood groups. Other blood group systems exist and, to date, researchers have identified around 300 minor blood groups.

The four different blood groups in the ABO system are A, B, AB and O.

ABO blood groups

How are blood groups inherited?

A person’s blood group is determined by a pair of genes, one gene inherited from each parent.

How are blood groups identified?

Each blood group is identified by its own set of molecules (called antigens), which are located on the surface of red blood cells. When a person needs a blood transfusion, the donated blood must match the recipient’s blood or complications will occur.

The Rh type blood factor

A person’s blood type used to be called their ‘Rhesus type’ but now we say ‘Rh type’. Our Rh type is determined by a different pair of genes (again, one inherited from each parent). Blood is either Rh-positive or Rh-negative, depending on whether or not certain molecules are present. A person who is Rh-negative will experience a severe immune-system reaction if Rh-positive blood gets into their bloodstream.

ABO donation path

Blood types

Your blood type is determined by antibodies – proteins in your blood that search out foreign substances, such as germs – and by proteins found on the surface of the red blood cells.

Blood transfusion

A blood transfusion is the transfer of blood or blood components from one person to another. Transfusions are of red cells or other components such as plasma or platelets. O negative red blood cells can be given to anybody if necessary, but it is always preferable to match the exact blood group.

ABO blood groups Resources
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