Delayed hemolytic transfusion reactions. Evidence for complement activation involving allogeneic and autologous red cells

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Abstract
Twenty‐six patients with delayed hemolytic transfusion reactions (DHTR) were investigated. The reaction of hemolysis often was concealed by other disorders that were usually associated with signs of hemolysis or blood loss. Coating of red cells was analyzed with regard to IgG and/or complement bound in vivo. Although many of the alloantibodies involved (K [8]; E [5]; Fya [2]; Fyb [2]; D [1]; c [1]; multiple [7]) are usually thought to be incapable of complement activation, a strongly positive direct antiglobulin test (DAT) due to C3d was found in all cases. On first examination after transfusion, C3d was present on circulating red cells in large amounts and remained discernible for weeks and even months. IgG on red cells was detected by the DAT in only 10 out of 26 cases. By means of a sensitive radioimmunoassay, IgG was demonstrated in 16 out of 17 cases, but usually in small quantities. Despite the low IgG concentrations, the causative alloantibodies could be eluted in 25 of 26 cases, and, as shown by sequential investigations, in six cases were recoverable from circulating red cells for over 100 days posttransfusion. Since the antiglobulin reactions due to anti‐complement were usually strong, not of the “mixed‐ field” type, and in some cases remained detectable on circulating red cells for months, we conclude that complement is regularly activated in DHTR and binds not only to donated but probably also to autologous red cells.