Presence of the red cell alloantibody anti-E in an 11-week-old infant

The development of red cell (RBC) alloantibodies in infants less than 4 months of age is believed to be rare. Though there are no well-documented published accounts, the formation of alloanti-E in a multiply transfused 11-week-old infant is reported here. The infant, blood group B, D +, developed necrotizing enterocolitis and renal failure requiring 31 transfusions of washed and unwashed RBCs (group B and group O), as well as fresh-frozen plasma and platelets. Six weeks after the first blood transfusion, alloanti-E was detected. The anti-E weakly agglutinated R2R2 screening RBCs at 37 degrees C and sensitized these RBCs to react with anti-IgG. The infant's RBCs were typed as E-. Passive transfer of alloanti-E was ruled out by the negative antibody screening tests of each donor unit and the absence of any RBC alloantibodies in the mother's serum. Stored samples of the infant's sera were tested, and anti-E was shown to be present approximately 11 days after exposure to a known E+ RBC unit. The appearance of alloanti-E in this time frame is consistent with a secondary immune response. Primary immunization most likely took place in the first 4 weeks of transfusion therapy.