Eleven years of alloimmunization in 6496 transfused patients with sickle cell disease in France.

Red blood cell (RBC) transfusion is a major therapy for sickle cell disease (SCD). Patients are at risk of forming antibodies to RBC antigens which can result in the impossibility to find compatible units and cause hemolytic transfusion reactions. This retrospective study investigates the evolution of RBC consumption, the frequencies, specificities and chronology of appearance of antibodies in a population of patients consistently receiving RH-K matched RBC units (RBCu) from a predominantly European donor population. Over the 11 year period in the Paris area, 6496 patients were transfused at least once for a total of 239944 units. Antibodies were made by 1742 patients. The first antibodies of a patient were predictive of subsequent immunization. By the 17th RBC unit transfused (by the 20th, excluding warm autoantibodies), 75% of patients who would make antibodies had made their first. By the 16th, 90% who would make antibodie(s) to a high frequency antigen had made their first antibody to these antigens. Females made their first antibodies slightly earlier than males. Multitransfused patients (>50 units) had a higher immunization prevalence than rarely transfused patients (<12 units) but fewer clinically significant antibodies. Patients with SCD and prophylactic RH-K matching not immunized by the 20th RBCu are likely to have a low alloimmunization risk (to antigens other than RH-K), i.e. be low responders, especially relative to the most clinically significant antibodies. This number of 20 units is a point before which close monitoring of patients is most important, but remains open to future adjustment.