title: The risk of alloimmunization to c (Rh4) in R1R1 patients who present with anti-E.
abstract: BACKGROUND
  Because the Rh antigens E (Rh3) and c (Rh4) are relatively immunogenic, it has been suggested that R1R1 (E-, c-) patients who present with anti-E alone receive prophylactic c- (Rh: -4) red cell transfusions.
  
  
  METHODS
  To determine the utility of this approach, the transfusion records of 100 consecutive R1R1 patients with anti-E identified over a 6-year period were reviewed.
  
  
  RESULTS
  Thirty-two (32%) had anti-c concurrent with anti-E. Twenty-seven of the 68 patients who presented with anti-E alone received random (i.e., not typed for c [Rh4]) red cell transfusions. Five (18.5%) of the 27 subsequently developed anti-c 13 to 193 days (mean, 50) after transfusion of 2 to 14 (mean, 8) red cell units. None of the five had clinical evidence of hemolysis that could be attributed to a delayed hemolytic transfusion reaction. Twenty-two (81.5%) of the 27 failed to develop anti-c even after transfusion of 1 to 41 (mean, 9; median, 7) red cell units.
  
  
  CONCLUSIONS
  The overall rate of immunization to c (Rh4) antigen in R1R1 patients with anti-E was 37 percent. Production of anti-c following transfusion to R1R1 patients with anti-E occurred in 18.5 percent of the cases in this series, which could have been avoided by the prophylactic use of R1R1 (E-, c-) blood for transfusion. The prophylactic use of c- (Rh: -4) blood in this patient population may be justified by the high immunization rate and the potential risk of delayed hemolytic transfusion reaction.
authors.affiliation: Johns Hopkins Hospital Blood Bank, Baltimore, Maryland.
authors.forename: R S
authors.initials: RS
authors.lastname: Shirey
authors.forename: R E
authors.initials: RE
authors.lastname: Edwards
authors.forename: P M
authors.initials: PM
authors.lastname: Ness
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001787:Blood Group Incompatibility / Q000276:immunology*; D001803:Blood Transfusion; D005260:Female; D006801:Humans; D007518:Isoantibodies / Q000097:blood; D007519:Isoantigens / Q000276:immunology*; D008875:Middle Aged; D012203:Rh Isoimmunization; D012204:Rh-Hr Blood-Group System / Q000276:immunology*
chemical_list: D007518:Isoantibodies; D007519:Isoantigens; C033242:RH-antibodies; D012204:Rh-Hr Blood-Group System