Prevalence of Nonrepresentation of Human Leukocyte Antigens and Alleles in Panel-reactive Antibody and Single-antigen Bead Assay Panels – In a Multiethnic Indian Population in a Metropolitan City

Introduction: Identification and monitoring of HLA antibodies against the Donor HLA antigens are one of the ways to risk stratify and monitor an allograft. Panel reactive antibody (PRA ID) assay and single antigen bead (SAB) assay serves as an extensive virtual cross-match tool to help a laboratory and a clinician treat a patient. Material and Methods: 830 consecutive patients representing multi-ethnic Indian population, referred for HLA typing and PRA ID and SAB analysis in the period of August 2021 to December 2024 were studied. Their HLA antigens and alleles were analysed for their representation on the beads in these solid phase assays from both the existing vendors A and B. Intermediate resolution HLA typing of 6 Loci A, B, C, DRB1, 3, 4, 5, DP and DQ by SSOP method performed on Luminex platform. Results: A total of 247 distinct alleles were identified in the study population. Among these, 55.4% ( n = 137) were presented on PRA ID Panel of Vendor A and 50.6% ( n = 125) in PRA ID panel of vendor B. 58.7% ( n = 145) of alleles were represented in SAB Panel of Vendor A and 53.8% ( n = 133) on SAB Panel of Vendor B. Conclusion: Our study highlights the limitation of relying on the presently available SAB panels to identify the presence of DSAs. One cannot rely on virtual crossmatch performed with existing SAB panels due to the non-representation of locally prevalent or unique alleles in our population. Consequently, we advocate combining SAB profile with physical crossmatching when encountering mismatched alleles that lack representation.