The risk of alloimmunization to c (Rh4) in R1R1 patients who present with anti‐E

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. STUDY DESIGN AND 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. CONCLUSION: 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. 1994 AABB