In Reply

Abstract

We thank Cid and Laia for their interest in our article that described a prospective evaluation of a transfusion policy of D+ red blood cells (RBCs) into D− patients.1 They raise three issues: The main aim of our study was to prospectively evaluate the outcome of a policy for the use of D+ RBCs in D− patients and to report on the amount of D− RBCs saved as well as the incidence of hemolytic reactions. D− alloimmunization was not our main objective. As noted by Lozano and Cid2 in nonimmunosuppressed individuals, anti-D formation after D+ RBC transfusion usually occurs after 4 weeks. Just 19 percent of 34 anti-D formers were studied for alloimmunization between 2 days and 4 weeks. Three of those 6 patients were male without anamnestic signs of a sensitization (blood transfusions, etc). Therefore, we could not exclude a secondary D immunization in only 3 patients. The mean number of D+ RBCs transfused in anti-D nonformers was higher than in anti-D formers (4.1 ± 2.2 vs. 3.2 ± 2.4, data not reported). But these mean values are not comparable because if the seroconversion was detected the patient received D− RBCs in the following transfusions. In addition, the Cox proportional hazard model employed by Frohn and coworkers3 to calculate the probabilities of antibody formation with different numbers of transfused RBC units did not show statistical difference. In our study, the 88 percent of anti-D formers developed anti-D during the first 4 units of RBC. From our point of view the conclusion should be “those patients who do not develop anti-D during the transfusion of the first 4 units of RBC have a far lower probability of former anti-D.” Finally, we agree with the concept of D− reported by Young and colleagues.4