Rh factor, refers to the D antigen, found on the erythrocytes of 85% of the Caucasian population and varying frequencies in other populations. Rh-positive or Rh-negative refers to the presence or absence of the D antigen, but many other antigens are also part of this system, most notably C, c, E, and e. D is the most immunogenic antigen outside the ABO system; therefore D-negative recipients should receive only D-negative donor blood to avoid exposure and immunization to D. D-negative mothers who carry D-positive infants should receive Rh immune globulin to prevent immunization during pregnancy and delivery. Also called Rhesus factor. See also anti-Rh agglutinin, erythroblastosis fetalis, RhO(D) immunoglobulin.
