Blood groups

 

Blood groups - Systems of classifying blood according to the different marker proteins (antigens) on the surface of red blood cells and antibodies in the plasma. These antigens affect the ability of the red blood cells to provoke an immune response. There are 2 main blood grouping systems: the ABO system and the rhesus system.

In the ABO system, the presence or absence of 2 types of antigen (named A and B) on the surface of the red blood cells determine whether a person’s blood group is A, B, AB (which has both A and B), or O (which has neither A nor B). People with the A antigen (group A) have anti-B antibodies; people with the B antigen (group B) have anti-A antibodies; those with both antigens (blood group AB) have neither; and those with neither antigen (group O) have both.

The rhesus system involves several antigens, the most important of which is factor D. People with this factor are Rh positive; those without it are Rh negative. The importance of the Rh group relates mainly to pregnancy in Rhnegative women, since, if the baby is Rh positive, the mother may form antibodies against the baby’s blood (see rhesus incompatibility).

A person’s blood group is inherited and may be used in paternity testing. Genetic analysis allows identification of the blood of a criminal suspect with virtual certainty (see genetic fingerprinting).