P152 Prozone phenomena may skew the strength of Donor Specific Antibody (DSA)

Abstract

Aim Positive Complement Dependent Cytotoxicity (CDC) and Flow Cytometry Crossmatch (FCXM) usually correlate with high titer of Donor Specific Antibodies (DSA). Now a days assignment of relevant DSA is based on solid phase assay (SPA), in which false low/negative results can be observed due to prozone effect. Here we present three cases underwent a workup for living related kidney transplant that their crossmatch data does not correlate with the single antigen (SA) Median Fluorescent Intensity (MFI) value. Method B cell and/or T cell AHG-CDC, FCXM and antibody identification by SPA were performed for three living related pairs. Results Two patients show positive T cell AHG-CDC crossmatch and one shows positive B cell CDC crossmatch with 8 reaction strength at 1:8 dilution and positive FCXM with very high Median Channel Shift (MCS). However the DSA result was negative for one patient and the other two patients showed A2 (891 MFI) and DQ6 (1299 MFI) respectively. The SA testing indicated possible skewed MFI value, therefore all serum were diluted 1:4 to overcome a prozone effect if present. Conclusion MFI value of the SPA was not correlated with the high MCS and positive CDC crossmatch in undiluted serum due prozone phenomena of high antibody concentration. Therefore serum dilution should be considered if strong crossmatch reactivity observed.