To the Editor:
We read with interest the article by González-Porras and colleagues1 about a prospective evaluation of a transfusion policy of D+ red blood cells (RBCs) into D− patients. We would like to address three important findings of the article.
First, the authors were able to evaluate for potential alloimmunization 159 D− patients who received D+ RBCs and they identified 34 (21.4%) patients who formed anti-D. However, 19 percent of those patients had a serologic follow-up of between 2 days and 4 weeks. It is important to guarantee that anti-D formation is the result of a primary immunization by D+ RBCs. In nonimmunosuppressed individuals, the earliest time at which anti-D can be detected in primary immunization ranges from 4 to 10 weeks and the production of anti-D within 2 weeks of a first stimulus has been observed only after the injection of specially treated D+ RBCs.2 Therefore, it is not possible to exclude a secondary D immunization in 19 percent of patients and we believe that the true primary immunization in the study by González-Porras and colleagues is lower than reported.
Second, the authors only reported the mean number of D+ RBC units (3.2 ± 2.4 units) received by the group of patients who formed anti-D. However, it would be also desirable to know the mean number of D+ RBC units transfused to the group of patients who did not form anti-D. This is because there are published data where the mean number of D+ RBC units transfused was lower in the anti-D former group when compared with the group of patients who did not form anti-D, which would suggest an inverse correlation between probability of antibody formation and number of D+ RBC units given.3
Finally, Gonzalez-Porras and colleagues reported 125 (78.6%) D− patients who did not form anti-D after receiving D+ RBC units and 83 percent of them were followed more than 4 weeks.1 It is important to point out the concept of D−, nonresponder patients who have not been fully characterized by anyone and remains one of the important unresolved issues in Rh biology.4