Prevalence and Specificity of Red Blood Cell Alloimmunization Among Transfusion Recipients in a Portuguese Hospital

Background/Aim: The transfusion of red blood cells (RBCs) is a vital and widely used support therapy. Although often lifesaving, it carries certain risks, as it exposes the patient to alloimmunization due to exposure to various antigens. Despite its importance, the relative frequency of RBC alloantibodies within the general patient population in Portugal has not been extensively studied. This study aimed to investigate the prevalence of RBC alloimmunization in patients attending a Northern Portuguese Hospital Center. Patients and Methods: We conducted a 3-year retrospective study to investigate the incidence of RBC alloimmunization in patients who received RBC transfusion at a hospital center in Northern Portugal and characterized the target population according to demographic data; ABO, Rh, and Kell blood groups; associated pathology; hospital department; and number of RBC transfusions. Results: The alloimmunization rate was 1.3% in the study population of 4,079 patients who received RBC transfusion, with the most common antibody being anti-K (18.5%), followed by anti-Lua (13.0%), and anti-E (11.1%). Among the 54 patients that developed alloimmunization, 75.9% developed only one alloantibody, 9.3% presented two alloantibodies, and only 1.9% of the cases developed three alloantibodies; specificity was not identifiable for the remainder. Hematological malignancies were the most frequently observed pathology in the alloimmunized population (25.9%), with myelodysplastic syndrome being the most common (13.0%). Conclusion: This study demonstrates the importance of characterizing alloimmunized populations to identify high-risk groups. Based on this understanding, it becomes feasible to implement targeted preventive measures to reduce alloimmunization rates and optimize the use of available resources.