False-positive reactivity of anti-human leukocyte antigen antibodies detected using the single-antigen bead assay

The single-antigen bead assay (SABA) demonstrates high sensitivity and specificity for detecting anti-human leukocyte antigen (HLA) antibodies. However, SABA may produce false-positive results for anti-HLA antibodies. Herein, we analyzed the data of patients with complement-dependent cytotoxic crossmatch⁻/flow cytometric crossmatch⁻/SABA^+/− results to determine false-positive results for anti-HLA antibodies. We also determined the prevalence of false-positive results by comparing false-positive data from our laboratory and national allele frequency data obtained with high-resolution HLA typing. For HLA-A, -B, -C, and -DR, a ratio of positive frequency to allele frequency of ≥3 in our laboratory was considered a false-positive result. For HLA-DQA1/DQB1 and HLA-DPA1/DPB1, we considered the positive frequency of ≥3 as a false positive result due to lack of haplotype frequency data. SABA results from 284 patients (78.0%) demonstrated false reactivity. The antibody against HLA-C*17:01 displayed the highest frequency ratio (298.3). If false-positive reactivity is suspected, results should be confirmed using different methods. If confirmation tests are unfeasible, comparing the allele frequency with the positive rate of detected anti-HLA antibodies and using a ratio ≥3 may facilitate the interpretation of SABA results. The positive rate of anti-HLA antibodies can be validated using the HLA allele frequency of the population to determine false-positive results.