Development of an Algorithm for Interpretation of HLA Single-Antigen Bead–Based Antibody Identification Test and Report Form

Background: Single antigen bead-based antibody identification test (SAB ID), including donor-specific antibodies (DSAs), and support desensitization, post-transplant risk monitoring, and allocation by using virtual crossmatch (VXM) and calculated panel reactive antibody (cPRA).We assessed the practice in Korean institutions and developed a basis for harmonization.Methods: A 50-item questionnaire (eight domains from specimen selection to interpretation/reporting) was developed using literature review and expert consensus and sent to 27 institutions in the national HLA antibody external quality assessment program and major transplant centers.The responses were summarized descriptively, and a stepwise interpretation algorithm and reporting guidance were formulated.Results: Twenty-five institutions responded (92.6%); 23 performed SAB ID testing, and 22 performed HLA typing.Most (77.3%) used lowto-intermediate sequence-specific primer PCR/sequence-specific oligonucleotide probe hybridization typing for HLA-A, HLA-B, HLA-DRB1, and HLA-DQB1, whereas locus coverage (HLA-C, HLA-DQA1, HLA-DPB1, and HLA-DRB3/4/5) varied.All laboratories used normalized mean fluorescence intensity (MFI), but the positivity cutoffs, MFI category definitions, and reporting of mean versus maximum MFI differed widely.Prozone or interfering reactions were reported by 43% laboratories, and 69.6% showed that EDTA-treated serum was the default specimen.Based on these findings, we proposed harmonized practices: EDTA-treated specimens, a basic MFI cutoff of 1,000 with optional lower-range DSA reporting, standardized locus coverage, explicit DSA and separate class I/II cPRA reporting, and documentation of HLA imputation and additional typing.Conclusions: SAB-based HLA antibody identification shows substantial inter-institutional heterogeneity in Korea.The proposed interpretation algorithm and reporting recommendations may improve inter-laboratory comparability, enhance clinician communication, and support future VXM implementation in the Kidney Allocation System (KAS) of Korea.