Relative sensitivity of direct antiglobulin test, antibody's elution and flow cytometry in the serologic diagnosis of immune hemolytic transfusion reactions.

BACKGROUND AND OBJECTIVE Current immunohematology practice dictates that serologic diagnosis of immune hemolytic transfusion reactions (IHTR) is based on the finding of a positive post-transfusion direct antiglobulin test (DAT). However, since DAT may fail to detect antibody-coated cells when they constitute a minor population amid a large number of non-sensitized ones, we investigated whether antibody detection in eluates or by flow cytometry is more sensitive than DAT in this context. DESIGN AND METHODS Ten samples of red blood cells sensitized with allo- or autoantibodies were diluted in non-sensitized red blood cells to final concentrations ranging from 10% to 0.1%. DAT, antibody detection in eluates, and immunofluorescence by flow cytometry were performed on each mixture. RESULTS DAT failed to detect sensitized cells in all but two cases in that only the 10% dilution yielded a positive DAT. Antibody detection in eluates and by flow cytometry was able to detect up to 1% sensitized cells in most cases. INTERPRETATION AND CONCLUSIONS Antibody detection in eluates and by flow cytometry is more sensitive than DAT for detecting minor populations of IgG-coated cells. These techniques should be included in the routine investigation of suspected cases of IHTR.