Severe anaphylactic reactions following transfusions of platelets to a patient with anti‐Ch

The high-frequency Chido (Ch) antigen, found predominantly in plasma, is a determinant of the C4d fragment of the C4 molecule and is acquired by red cells during in vivo complement activation. Antibodies are made by Ch- people who lack C4S. It has often been reported that anti-Ch (and anti-Rg) do not cause hemolytic transfusion reactions. Reported here is a case of a transfusion reaction caused by anti-Ch. The antibody did not cause red cell destruction, but did cause a life-threatening anaphylactic reaction during transfusion of plasma proteins in pooled platelets. The antibody was of the IgG4 subclass and might have caused a short-term, sensitizing anaphylactic response. This case, and one previously reported in which a patient with anti-Rg experienced a severe reaction to fresh-frozen plasma and a plasma derivative, illustrates that these antibodies can cause severe, life-threatening reactions in patients who receive plasma-containing components.