The incidence of development of irregular red cell antibodies in patients with sickle cell anemia.

Two hundred and forty-five patients with SS hemoglobinopathy were screened for alloimmunization; they had all been transfused previously. Their median age was 10 years. Nineteen patients (7.75%) were found to be sensitized to various red cell antigens. The median number of transfusions received by sensitized patients was 23 compared to three in the unsensitized group, indicating an increased risk with more transfusion exposures. Thirteen sensitized patients were re-exposed to transfusion and four (30%) developed new alloantibodies. Once immunized, the risk of developing more alloantibodies on re-exposure did not increase with increasing number of exposures. The most frequently observed alloantibody was anti-K, accounting for 38 percent of all instances. Anti-Lea and -Leb were next in frequency (24%); Rh antibodies were seen in 14 percent of cases. Children with sickle cell anemia who were multiply transfused had a low frequency of alloimmunization. Responders had an increased rate of further sensitization which did not increase with number of subsequent exposures. Phenotypically matched blood is probably not warranted in most patients receiving transfusions for sickle cell anemia.