Lower alloimmunization rates in pediatric sickle cell patients on chronic erythrocytapheresis compared to chronic simple transfusions

BACKGROUND: Erythrocytapheresis (ECP), automated red blood cell exchange, is increasingly being used for chronic transfusion therapy in sickle cell disease (SCD) as it is an isovolumetric transfusion, is more effective in lowering hemoglobin (Hb)S, and can limit iron overload. Because ECP requires increased blood exposure compared to simple transfusions there is concern for increased transfusion complications, including alloimmunization. We compared alloimmunization rates between patients receiving simple or exchange chronic transfusions. STUDY DESIGN AND METHODS: Data were retrospectively collected for 45 SCD patients (n = 23 simple, n = 22 ECP) on a chronic transfusion program as of December 2010 to determine the rate of antibody formation (antibodies formed per 100 units transfused). RESULTS: The 45 patients received 10,949 units and formed six new alloantibodies during the study period (1994-2010); therefore, the overall alloimmunization rate was 0.055 alloantibodies per 100 U. There were three antibodies formed in three patients on ECP, one allo (anti-rhi) and two autoantibodies. There were six antibodies in four patients on a simple transfusion program, five allo (anti-Lea, M, D, C, and Kpa) and one autoantibody. The ECP group received significantly more blood (338.5 units/patient vs. 152.2 units/patient, p = 0.001). The rate of antibody formation (auto plus allo) was 0.040 antibodies per 100 U in the ECP group and 0.171 antibodies per 100 U in the simple transfusion group (p = 0.04). The alloantibodies formed per 100 units was 0.013 in the ECP group and 0.143 in the simple transfusion group (p = 0.03). CONCLUSION: Chronic ECP should be considered in patients requiring optimal management of HbS levels and iron burden. Concerns about increased alloimmunization with ECP may be unjustified.