UCSF

Single Antigen Bead (SAB) assays are the cornerstone of HLA antibody detection in transplant immunology. However, discrepancies in mean/median fluorescence intensity (MFI) values between the two commercially available assays raise concerns about result interpretation and assay interoperability. Using 281 well-characterized serum samples positive for a broad range of HLA antibodies, we evaluated 118 core HLA antibody specificities for MFI concordance across platforms. Cell-binding ability of specific HLA antibodies was evaluated by T- and B-cell flow cytometric crossmatch (FCXM) in 613 single antibody-targeted pairings. Strong correlations were observed for HLA-A, -B, and -DR antibodies between platforms. Correlations for HLA-C, -DQ and -DP were moderate to poor. Discordance often linked to differences in allele composition-particularly for DQ and DP, which use distinct α/β chain pairings. FCXM correlated well with MFI for Class I antibodies, but correlation was limited for Class II antibodies. Despite design differences, the assays were largely concordant for most HLA specificities. Used together, they offer complementary insights, particularly for challenging loci such as HLA-C, -DQ, and -DP. However, for antibody profiling in transplant candidates, the lack of correlation for the latter loci could make accurate data interpretation difficult if the bead sets and vendor kits were used interchangeably.