P148 Precise definition of HLA-antibody by ruling out false positive reactivity from luminex single antigen assay in supporting succesful thoracic organ transplantation

Aim False positive antigen specificities (FPAS) from the Luminex Single Antigen (LSA) Assay are difficult to identify due to multiple interfering factors and various corresponding resolving approaches. Over calling antibodies limits a patient’s access to deceased donor organs and can result in erroneous immune therapy. Here we report how to properly identify and resolve FPAS from LSA assays to precisely provide HLA-antibody results in supporting Thoracic Organ Transplantation (TOT). Methods We retrospectively studied 66 TOT cases that had suspected FPAS reactions with LSA assays. The initial antibody work up was tested by LSA and FlowPRA Screening Beads. Discordance between the two assays and/or ambiguity were verified by Luminex Phenotype Beads. LSA was used for all antibody follow up. If an obvious antibody increase was observed, further investigation for sensitizing events and/or possible interfering medication (such as IvIg), warranted additional testing. Detailed approaches for FPAS identification and resolution are listed in Table 1a. Results Of the 66 FPAS cases, 56 (85%) were caused by denatured antigen (dAg) and 10 (15%) were due to IvIg infusion. The distribution of complete FPAS and partial FPAS (the mixture of true positive and FPAS) from dAg and IvIg were almost equal, 54% vs 46% and 50% vs 50%, respectively. The FPAS dAg patterns with highest occurring frequencies were Cw1, Cw12, Cw15 (27%) from class I and DP1, DP11, DP13, DP6, DQ4 (34%) from class II. The elimination of FPAS reduced the average PRA by 67% from dAg and 78% from IvIg interference. 22 cases received TOT after FPAS were ruled out (Table 1b). Conclusions FPAS is the prevalent issue of LSA when false negativity is eliminated by serum EDTA treatment. Alternative assays by multiple platforms, supplementary LSA data analysis, and referencing clinical records are warranted for ruling out FPAS. This provides precise antibody testing results for successful access to TOT.