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 Rh- negative 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).
Blood groups |
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