Autologous crossmatches: How useful are they in the evaluation of positive donor flow cytometric crossmatches?

Abstract

Aim Our laboratory testing algorithm includes autologous flow cytometry crossmatch (auto FCXM) on all positive (pos) donor/allo FCXM. Depending on the assessed immunological risk of the donor/recipient pair and the availability of the recipient sample, the auto FCXM may be set up on call or as a STAT test. The aim of this study was to evaluate the utility of auto XM to aid in the investigation of pos allo FCXMs. Methods FCXMs performed between January and June of 2014 were reviewed (n = 214); negative (neg) allo-FCXMs were excluded from this analysis as no auto FCXM was performed. All FCXMs were performed using a plate based method; all cells were treated with pronase. Donors and recipients were typed for all loci including HLA-C∗, -DQA1∗, -DPB1∗ and -DPA1∗ by rSSO. Positive FCXMs were further examined by LABScreen® single antigen beads (SAB). There were 23 pos allo FCXM results but auto-FCXM could not be performed on 4 recipients. Thus auto XM data are available on 19 recipients. Results Of the 19 pos allo FCXMs, only 4 auto FCXMs were positive (21%) with three demonstrating preferential T cell reactivity. There were 15 results that were allo FCXM pos/ auto FCXM neg. SAB testing revealed that seven allo-FCXM results were explained by HLA DSA (37%), and 8 had no DSA detected (42%). Conclusions Since 79% of the autologous crossmatches were negative and all were followed up with antibody screening, it may be reasonable to remove autologous crossmatching from our testing algorithm. We are currently performing a cost analysis of alternative testing algorithms to include urgent SAB testing. As virtual crossmatching becomes more prevalent, it is increasingly important to evaluate current antibody identification as reflected by the unexpected positive donor XM results due to new, previously undetected DSA. The auto FCXM did not aid in the explanation of the positive allo FCXM without DSA and the cause of reactivity remains unclear in these cases. L. Hidalgo: Speaker’s Bureau; Company/Organization; Thermo-Fisher/One Lambda Inc.