Red blood cell alloimmunization in transfused patients with myelodysplastic syndrome or chronic myelomonocytic leukemia

BACKGROUND: Red blood cell (RBC) alloimmunization is a major problem in chronically transfused patients because of the risk of hemolytic reactions and limited availability of compatible blood. This study was aimed at determining the characteristics of RBC alloimmunization in transfusion‐dependent patients with myelodysplastic syndrome or chronic myelomonocytic leukemia (MDS/CMML). STUDY DESIGN AND METHODS: The transfusion and clinical records of all patients with MDS/CMML seen at our hospital from 1990 to 2009 were reviewed. The cumulative incidence of RBC alloimmunization was calculated by taking death as a competing risk. Incidence rates were compared by Poisson multivariate regression. RESULTS: A total of 272 patients were included. Median age was 74 years; 55% were men and had received a median of 33 (range, 4‐421) RBC units. Forty‐two (15%) patients formed 81 alloantibodies and seven autoantibodies. Three additional patients developed autoantibodies without alloantibodies. The incidence rate of RBC alloimmunization was 1 per 10.5 person‐years and was independent of sex, age, and MDS diagnostic category. The cumulative incidence of alloimmunization increased with the number of RBC transfusions, reaching a plateau at 19.5% after 130 RBC units. The most common antibody specificities were Kell (26 cases), E (19), c (5), and Jk^a (5). In 26 (62%) of the 42 alloimmunized patients, only the Rh system and Kell were involved. CONCLUSION: RBC alloimmunization occurs in 15% of MDS/CMML patients on chronic transfusion support and mostly involves the Rh system and Kell. Transfusing these patients with extended antigen‐matched blood, including Kell and CcEe antigens, would presumably reduce the RBC immunization rate.