PB2309 INCIDENCE OF ALLOIMMUNIZATION IN SICKLE CELL DISEASE: EXPERIENCE OF A CENTER IN LISBON

Background: Nowadays, red blood cell (RBC) transfusion is an indispensable option for the treatment and prevention of chronic complications of sickle cell disease (SCD). In SCD patients it has been reported at a rate of 18–76% of alloimmunization after transfusion. It has also been suggested, that transfusion is related to the formation of RBC autoantibodies, especially in patients with hemoglobinopathies. Interestingly, some authors correlate higher susceptibility to allo and autoimmunization in patients without the spleen. That could be one of the explanations why SCD patients have a higher incidence of RBC immunization. Aims: To determinate the rate of alloimmunization among the transfused SCD patients residing in Lisbon. The other objectives were to clarify among the same study population the incidence of positive direct antiglobulin (DAT) test and spleen absence and correlate both with alloimmunization. Methods: The subjects for the study were selected from the adult patients (≥18 years of age) of a tertiary hospital in Lisbon, between 01‐01‐2017 and 20‐02‐2018, that were transfused at least one time and monitored for the presence of irregular antibodies. A total of 61 patients met the inclusion criteria. Most of the routine immunohematological tests, i.e. blood group typing, indirect antiglobulin test (IAT) and DAT, were done using a microtube gel technique. Moreover, clinical assessment of the spleen status (absence or presence) were obtained from imagiological data. Results: In our study, we obtained a rate of alloimmunization of 21,3% (N = 13). 40% of the transfused SCD (N = 22) have in DAT positive and 50% of those/these have alloantibodies. We found in our population a significant association between positive DAT with alloimmunization (p < 0.001). In 58 patients we succeed in obtaining their spleen status and among those without a spleen (N = 36) 25% became alloimmunized. Summary/Conclusion: In our study, the risk of alloimmunization was higher in patients who received more than 20 red blood cell units. Our alloimmunization rate is in agreement with the literature as well as the significant association of DAT with alloimmunization. Interestingly, 50% of those patients with DAT positive also have alloantibodies, supporting the idea that those patients develop autoantibodies due to transfusion therapy. This fact advocates some plausibility in screening for autoantibodies at regular intervals prior to each transfusion. There was no significant correlation between the presence or absence of a spleen and alloimmunization (p = 0.7475). In conclusion, this study is one of the few to approach the rate of alloimmunization in SCD patients. Therefore, it is necessary to have further studies in Portugal in order to study and to understand our heterogeneous SCD population.