2-P: COMPLEMENTARY TESTING USING SOLID PHASE AND FLOW CYTOMETRY TECHNOLOGIES PROVIDES ACCURATE ASSESSMENT OF PREFORMED DSA

Aim For the past two years, we have compared retrospective solid phase crossmatches (DSAXM) with flow crossmatching on all patients who were either transplanted or exhibited positive flow cytometry crossmatches (FXM) with deceased donors to determine the realtionship between the two XM assays. Methods An MFI cut-off of 4000 MFI was used in SAB testing for unacceptable antigens. Flow cytometry crossmatches were analyzed on a BD FacsCanto II flow cytometer (pronase-treated cells). DSAXM was according to the manufacturer’s procedure. Results We analyzed 734 solid phase crossmatch/flow crossmatch pairs: 421 TFXM/DSAIXM and 313 BFXM/DSAXM. 108 TFXM+ crossmatches were eliminated for the BFXM comparison to minimize the interference of Class I on the BFXM/DSAXM comparisons. We observed that for TFXM/DSA1XM there was a 77% agreement. 22% of the discrepancies were mediated by a false positive TFXM crossmatch, based on lack of DSA. 21 of the 75 FXMs in this group had channel shifts above 1000 (our cut-off is 120). The remaining 1% of the discrepancies were mediated by false positive DSA1XM (n = 5). We observed that for BFXM/DSAXM there was a 73% agreement. As seen with the TFXM/DSA1XM the majority of the discrepancies were due to false positive BFXM (19.5%). There were also more discrepant false positive DSAXMs (7.7%). Conclusions These data demonstrate that the DSA1XM reliably detects Class I antibodies, (however the DSA2XM does not reliably detect DQ antibodies.) In this study, the incidences of unexplained positive TFXM and BFXM were high: 22% and 20%, respectively. For BFXM/DSAXM comparisons, neither assay demonstrated a competitive edge. Since neither the flow assay nor the solid phase assay reliably predicts crossmatch outcomes, we continue to use both assays in a complementary fashion. Combining the solid phase technology (single antigen beads and the DSAXM) and flow cytometry crossmatching provides a better assessment of risk due to preformed donor-specific alloantibodies than either assay alone.