One of the most important human blood group systems. The system is based on the presence or absence of carbohydrate antigens A and B on the surface of red blood cells and antibodies against these in blood serum. A person whose blood contains either or both of these antibodies cannot receive a transfusion of blood containing the corresponding antigens as this would cause the red cells to clump (see agglutination). The table illustrates the basis of the system: people of blood group O are described as ‘universal donors’ as they can give blood to those of any of the other groups. See also immunity.
The ABO blood group system
Group | Antigens on red cell surface | Antibodies in serum | Blood group of people donor can receive blood from | Blood group of people donor can give blood to |
|---|
A | A | anti-B | A, O | A, AB |
B | B | anti-A | B, O | B, AB |
AB | A and B | none | A, B, AB, O | AB |
O | neither A nor B | anti-A and anti-B | O | A, B, AB, O |