P154 Variability in the sensitivity of the flow cytometric crossmatch

Aim The sensitivity of the flow cytometric crossmatch (FXM) is often variable across labs in the presence of weak donor specific antibodies (DSA). In addition, inter-laboratory variation to the interpretation of Mean Fluorescence Intensity (MFI) values escalates the potential for discordance. The aim of this study is to compare FXM results among laboratories and correlate the results with DSA strength. Methods The study collected and analyzed data reported by participants in the Flow and Virtual Crossmatch Exchange over a period of 4 years. Data collected included antibody specificities, MFI values, T- and B-cell positive cutoffs, mean channel shifts (MCS), and negative control MC. In addition, the coefficient of variations (%CV) were calculated using the center-specific MFI values to analyze the variability in the reporting of antibody strength among labs. Results A total of 24 cells were tested against 48 sera over 12 Exchanges for a total of 96 T/B flow crossmatches. Among the 96 FXM pairs, 84% of T-cell and 88% of B-cell crossmatches were reported with good agreement (u003e80%). Positive concordant T-cell crossmatches were observed in 92% (57/62) of cases when class I DSA were reported with MFI u003e3000. Positive concordant B-cell crossmatches were observed in 89% (49/55) of cases when class I and class II DSA were reported with MFI u003e5000. Conclusions The data shows there is good consistency in T/B Flow crossmatch outcomes among labs in the presence of moderate or strong DSA. However, when DSA strength is weak, the sensitivity of the flow crossmatch is more widely variable. In addition, center practice, such as cutoff values and the reporting of MFI values may influence FXM outcomes. Thus, educational activities should continue to provide standards for quality control for the FXM.