OR11: THE IMPORTANCE OF SURROGATE CROSSMATCHING IN ASSIGNMENT OF HLD-DQ ANTIBODIES

Although generalities can be made relative to antibodies against all MHC loci, for simplicity we have limited this study to anti-DQ antibodies. Since assignment of even one unacceptable DQ antibody can severely limit access to donors, our program instituted a policy of surrogate donor crossmatching to supplement single antigen testing. Surrogate donor testing by 3 color flow cytometry (our final crossmatch of choice) was performed when the assignment by single antigen testing was questionable. Questionable assignments were determined most often by MFI values below our threshold, but where there other indications (e.g.“stacking” of specificities and/or discrepancies between vendors) for the presence of antibody. Serum was analyzed by all Luminex-based products and follow-up occurred by 3 color flow cytometry on appropriate HLA-typed donors, using pronase treated cells. 103 patients were included in the surrogate crossmatch analysis. Two-thirds of the patients (69/103 = 67%) were negative in the B flow crossmatch. MFI values for this set ranged from 1518–8533. The remaining 34 patients had antibodies to DQ confirmed by positive flow crossmatches with MFI values ranging from 250 to >10,000. This data suggests that the correlation between MFI data and crossmatch outcome is poor, at least within the broad MFI range of this group of patients and demonstrates that additional testing (like surrogate crossmatching) is fully warranted in the assignment of unacceptable specificities. Failure to identify these “false” antibodies by crossmatch can hinder the ability of an individual to be given an opportunity for an organ offer.