P009 Concordance of virtual and physical crossmatch results with weak donor specific antibody

Abstract

Aim Virtual crossmatch is becoming more routine in some transplant programs. We interested into evaluate the concordance of crossmatch results and weak donor specific antibodies (DSA) using proficiency testing survey results. Methods Crossmatch results with weak DSA (1 K–2 K median fluorescence intensity (MFI)) were analyzed using ASHI AC and CAP MX1 & MX2 PT reports conducted between 2015 and 2017. Multi-antigen and Single antigen bead assays by Luminex were used for antibody (Ab) screening and Ab identification tests, respectively. Positive cut-off for Ab testing was 1000 MFI. Only T cell Flow cytometry (TFXM) results are presented. Results In ASHI survey, 8 out of 9 challenges with class I DSA ranged from 1 K to 2 K were resulted Negative TFXM. Four of them were not graded due to insufficient consensus. In CAP MX1 survey, 4 out of 9 challenges with weak class I DSA up to 2 K had Negative TFXM and rest of them resulted Positive TFXM. Five out of 9 challenges were not graded due to insufficient consensus. In CAP survey, the majority of labs (64%) reported Positive TFXM in one challenge with below threshold (MFI: 942–990) DSA to HLA-B7 (virtually negative). In contrary, the consensus was reached (>90% of labs) with Negative TFXM in another challenge with 2 K DSA to HLA-B27 (virtually positive). Of note, 2 sera presenting anti-HLA-B7 DSA with MFI-1093 and MFI-1407 resulted Negative (graded) and Positive (68% of labs) TFXM, respectively in 2 separate challenges. The similar cases were also observed in ASHI PT surveys. Conclusions Nearly 50% of crossmatches with weak DSA in PT surveys were not graded due to insufficient consensus. In addition, less concordant crossmatch results were observed with weak DSA. Our findings suggest that virtual crossmatches with weak DSA should be confirmed by physical crossmatches as possible.