Blood groups are genetically determined and each is characterized by the presence of a specific complex carbohydrate . About 200 different blood group substances have been identified and placed within 19 known blood group systems. The most commonly encountered blood group system is the ABO, or Landsteiner , system. Since these agglutinins are always present in the blood, in blood transfusion the donor blood must be compatible with the recipient's blood, i.e., the donor's blood must not contain antigen corresponding to the recipient's antibody. Other blood group systems, such as the MNSs, Lewis, Lutheran, and P systems, are not as important in transfusion because they act like true antigen-antibody systems, i.e., antibodies do not appear in blood plasma until the individual has been immunized by exposure to the other blood group antigens as in previous transfusions.
Immunization can occur by pregnancy as well as by transfusion.
Anthropologists use the frequency of occurrence of various blood groups as tools to study racial or tribal origins. Listing from Electric Library , a pay service. Copyright 2001 Infonautics Corporation . All rights reserved. Hauspie Speech Products N.V. All rights reserved.