Donor selecting avoiding unacceptable HLA antigens (UAs) efficiently facilities heart transplant without performing a final flow crossmatch (FCXM) prior to transplant. Luminex single antigen bead assay (LSA) can finely define HLA antibody (ab) specificities for determination of UAs. This study is to retrospectively evaluate the criteria used for heart transplant donor selection for the final FCXM performed in the past 5 years.

HLA abs were identified at neat and 1:16 dilution for each heart transplant candidate by flow HLA ab screening (flow PRA) and LSA. LSA was only performed at 1:16 dilution when flow PRA was positive at 1:16. HLA antigens to which abs were detected at neat but not at 1:16 were not considered as UAs and were not listed in UNET for donor selection.

To establish predictability of ab positivity at 1:16 based on MFI of abs detected at neat, data of HLA testing obtained from Jan. 2010 – Oct. 2012 were analyzed. Only abs with available MFI both at neat and 1:16 were included in the analysis. Data of FCXM and LSA obtained from Dec. 2006 – Nov. 2011 were used to correlate MFI level of LSA and positivity of FCXM caused by donor specific antibodies (DSAs). Statistical analysis was done by ROC analysis with SPSS software.

Total 5876 individual ab records with MFI values of both neat and 1:16 titration were available on 234 serum samples of 108 patients. ROC analysis, not differentiating class I and class II HLA antigens, demonstrated that the optimal cutoff of MFI of neat LSA to predict a positive LSA result at 1:16 titration was 6609 (by Youden index, sensitivity=73.1%, specificity=87.4%), or 5843 (by equal sensitivity and specificity (ESS), sensitivity=specificity=79.6%). Total 45 FCXMs were carried out with donors carrying DSAs, of which 26 (58%) were positive. ROC analysis showed the optimal cutoff MFI value of LSA for DSA to predict a positive B cell XM were 3999 (by Youden index), or 3140 (by ESS), to predict a positive T cell XM were 3999 (by Youden index), or 2726 (by ESS).

The criteria used to determine UAs for heart transplantation based on LSA 1:16 titration was equivalent to the MFI 6000 of abs at neat. However, a positive FCXM was predicted by an MFI 3000-4000 of abs at neat LSA. The difference could explain the observation of more than 50% positive FCXM with DSAs. Donor selection using UAs determined at 1:16 showed acceptable transplant outcomes regardless FCXM reactivity.

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