Introduction: The high sensitive single antigen bead assay (SABA) is often shown false reactivity for human leukocyte antigen (HLA) antibodies (Abs). Accurate interpretation for HLA Abs existing in sera of the patients awaiting or transplanted organ transplantation is important for donor selection and decision for clinical treatment. We investigated SABA data and method to discriminate falsely reactive HLA Abs from true positive HLA Abs.
Materials and Methods: Total 364 patients' data were analyzed. Patients awaiting organ transplantation were 282 (77.5%), and patients after transplantation were 82 (22.5%). Every sera from patient was tested not only SABA but also screening test with panel kit and complement binding assay (C1q assay, LABScreen Luminex kits, One Lambda, Canoga Park, CA, USA) to decide true or false reactivity. Positive rate of reactive HLA Abs and allele frequencies from high resolution HLA typing of our laboratory data were compared.
Results: In panel kit analysis, 28.3% (n=103) of patients were positive for Class I or Class II HLA Abs. Post-transplanted patients had higher positive rate of HLA Abs (39.0%) than patients awaiting transplantation (25.2%). False reactivity from SABA results were shown from 284 patients (78.0%). Although not statistically significant, the false positive rate of HLA Abs in post-transplanted patients was 81.7%, higher than 77.0% of patient awaiting transplantation.
Comparison with allele frequencies from our laboratory HLA typing (n=613 ~ 761), three-times higher frequent HLA Abs than HLA allele frequencies or over 3% of positive rate with 0% frequencies of HLA allele were HLA-A*02:03, A*11:02, A*33:01, A*66:02, A*80:01, B*08:01, B*14:02, B*15:02, B*15:12, B*15:16, B*18:01, B*38:01, B*45:01, B*47:01, B*51:02, B*55:01, B*82:01, C*02:02, C*12:03, C*16:01, C*17:01, C*18:01, DRB1*01:02, DRB1*03:02, DRB1*04:04, DRB1*08:01, DRB1*11:04, DRB1*14:02, DRB1*16:01, DRB1*16:02, DQ2 (DQA1*03:01/DQB1*02:01, DQA1*05:01/DQB1*02:01), DQ4 (DQA1*02:01/DQB1*04:01, DQA1*03:03/DQB1*04:01), DQ6 (DQA1*01:03/DQB1*06:03), DQ7 (DQA1*02:01/DQB1*03:01, DQA1*05:03/DQB1*03:01, DQA*06:01/DQB1*03:01), DQ8 (DQA1*03:02/DQB1*03:02), DQ9 (DQA1*03:02/DQB1*03:03), DP1 (DPA1*01:03/DPB1*01:01, DPA1*02:01/DPB1*01:01), DP5 (DPA1*02:02/DPB1*05:01), DP6 (DPA1*01:03/DPB1*06:01) and DP13 (DPA1*03:01/DPB1*13:01). Highest ratio of positive rate HLA Abs to allele frequencies was 298.3 of antibody against HLA-C*17:01.
Discussion: HLA Ab with higher detection frequency than allele frequency of population was considered false reactive antibody, because a possibility of exposure would be very low. In each laboratory, it will be helpful to validate the positive rate of HLA Abs detected in accordance with the HLA allele frequency of this population to determine the false reactive HLA Abs.
Conclusion: Comparing the allele frequency to the positive rate of detected HLA Abs and using a ratio of 3 or higher will help to interpret the SABA results.