Introduction: Human leukocyte antigens (HLA) crossmatch (XM) detects preformed donor-specific antibodies (DSA) that can cause antibody-mediated rejection, even at low titers. XM methods have evolved from complement-dependent cytotoxicity XM (CDCXM) to flow cytometry (FCXM) and virtual XM on Luminex platforms, enhancing sensitivity for low-level antibodies undetected by cell-based assays. This study aimed to evaluate XM results and correlate them with solid-phase assays (SPAs), including panel reactive antibody (PRA) screening, percentage, and single antigen bead (SAB) assays for HLA Class I and II. Materials and Methods: All incidental XMs performed between December 2020 and December 2024 were analyzed. Samples with concurrent or recent (within 1 month) PRA or SAB results were included in the study. CDCXM (antihuman globulin-enhanced) included T-cell, B-cell, auto, and allo XM with serial dilutions up to 1:8. Positive auto-XMs were dithiothreitol-treated, and pronase treatment was applied when a history of treatment with intravenous immunoglobulin or rituximab was present. SPAs were performed using One Lambda kits on the Flexmap three-dimensional Luminex platform. XM results were classified as true positive (TP), true negative, false positive (FP), or false negative (FN) after correlation with SPAs. Results: Among 544 patient samples (456 FCXM, 477 CDCXM), 89.1% were negative for both assays. Six cases were TPs (CDCXM + and FCXM + with DSAs). Notably, 57.9% of DSA-positive cases had negative CDCXM and FCXM, representing FNs. One CDCXM+/FCXM + case lacked DSA due to antigen nonrepresentation, and two were FPs from nonspecific antibodies. Conclusion: Cell-based assays alone may miss low-titer DSAs. Combining XM with solid-phase testing ensures accurate immune stratification before transplantation.
Tapiawala et al. (Thu,) studied this question.