P1583: transfusions in autoimmune hemolytic anemia: frequency and clinical significance of alloimmunization

Topic: 31. Transfusion medicine Background: Autoimmune hemolytic anemia (AIHA) is a rare and heterogeneous disease, ranging from mild to very severe forms; the latter may present acutely and require transfusion support. There are several concerns regarding the risk of transfusion reactions and alloimmunization, reported in about 1/3 of cases in historical series. However, data on their clinical impact are lacking, especially considering the evolving blood selection strategies in the last decades. Aims: To evaluate transfusion policy and the rate of alloimmunization in patients with AIHA. Methods: 103 AIHA patients who received at least one transfusion, from a series of 408 cases followed at a single center in Milan Italy from 1997 to 2022, were included. Patients were classified as warm (wAIHA), cold (cAIHA), mixed or atypical (negative direct antiglobulin test, DAT, or IgA positive AIHA). Clinical and laboratory features, DAT, indirect antiglobulin test (IAT), auto and alloantibody specificity were retrospectively registered. Number of red blood cell (RBC) transfusions, hematologic parameters pre and post transfusion as well as transfusion reactions were recorded. Results: We included 103 patients with a median age of 62 years (19-94), a slight female predominance, and a median follow up of 64 months (range 1-305). Most were diagnosed with wAIHA (54%), followed by cAIHA (33%) and mixed/atypical AIHA (13%). The median number of RBC units (RBCU) transfused was 4 (1 – 55, two patients were heavily transfused due to subsequent diagnosis of myelodysplasia). Median pre-transfusion Hb was 6.8 g/dL (2.7-8.6), LDH 441U/L (125-2875), and reticulocytes 153x10^9/L (3-354). Eight febrile transfusion reactions (7%) were registered, none hemolytic. Figure 1 depicts the trend in transfusion frequency and rate of alloimmunization among 408 patients along time: RBC transfusions progressively decreased from 53% to 20% over time, particularly after 2010. Moreover, the rate of alloimmunization steadily and gradually decreased dropping from 30% to 6%. Overall, anti-RBC alloantibodies were found in 20 patients (19%). The latter showed a higher transfusion burden compared with non-alloimmunized (median of 10 vs 3 RBCU, p = 0.01). Furthermore, they showed a lower Hb increase post transfusion [0.9 (0.2 – 3.5) vs 1.5 (0 - 7.1) g/dL, p = 0.05]. This was even more significant for those transfused before 2010 [0.7 (0.2 -1.7) vs 1.8 (0.4 - 4.5) g/dL, p=0.03] but not in the last decade (> 2010), possibly due to the improved quality of RBC unit selection and allocation. Notably, the alloimmunized group had a significantly higher number of transfusion reactions (20 vs 4%, p = 0.04). Relapsed/refractory patients had a higher transfusion burden and also increased rate of alloimmunization [median relapses in allo vs non-alloimmunized patients: [2 (0-13) vs 1 (0-8), p = 0.05]. Finally, similar distribution of sex, age, or AIHA type and for ABORh group were noted. Summary/Conclusion: These data show that RBC transfusions in AIHA lead to a median increase of 1g/dL of Hb, and are generally safe, with less than 10% of patients experiencing febrile transfusion reactions. The latter were more frequent in subjects developing alloantibodies, who also showed a reduced post transfusion Hb increase. Finally, we observed a decrease in the transfusion rate and in the frequency of alloimmunization over the last two decades, likely linked to the adoption of pre-storage leukoreduction, to the use of more restrictive Hb thresholds, and to the implementation of molecular typing of patients and donors.Keywords: Blood transfusion, Autoimmune hemolytic anemia (AIHA), Clinical outcome, Antibody