Transfusions in autoimmune hemolytic anemias: Frequency and clinical significance of alloimmunization

Background: Autoimmune hemolytic anemia (AIHA) may be associated with transfusion reactions and risk of alloimmunization. Objectives: To evaluate the transfusion policy and rate of alloimmunization and its clinical significance in AIHA. Methods: Data from 305 AIHA patients followed at a reference hematologic Center in Milan, Italy from 1997 to 2022 were retrospectively/prospectively collected (NCT05931718). Results: Overall, 33% patients required transfusions with a response rate of 83% and eight transfusion reactions (7%), none hemolytic. Alloantibodies were detected in 19% of patients, being associated with higher transfusion burden (p = 0.01), lower Hb increase post-transfusion (p = 0.05), and transfusion reactions (p = 0.04). Along decades, the rate of RBC transfusions decreased from 53% to 20% and that of alloimmunization dropped from 30% to 6% likely due to the adoption of prestorage leukoreduction, the use of more restrictive Hb thresholds, and the implementation of molecular typing. Conclusions: Severe symptomatic AIHA may be safely transfused provided appropriate matching of patients and donors.