P271 False positive HLA antibody tests can lose organ offers

Abstract

Aim The accuracy of HLA antibody testing is very important for entering UNOS Unacceptable donor antigens, evaluating organ offers by virtual and prospective crossmatch, and evaluating donor specific antibodies (DSAs) pre and post transplant. It is known that the Single Antigen Bead (SAB) assay can have HLA antibody false positives reactions, due to the exposure of cryptic, non HLA antigens, during the manufacturing process. This study was to determine the SAB false positive rate in our testing and evaluate how two other HLA antibody assays, FlowPRA Screen and LSPRA (phenotype bead), can help to improve the accuracy, by confirming or ruling out false positive SAB antibodies. Methods A Jan-March 2017 sample set of pre and post transplant patients with SAB HLA antibodies and LSPRA and/or FlowPRA confirmatory testing, was obtained from our HLA database. The three assays were compared to determine SAB false positive rate and how to improve the accuracy of this assay. Results Of 20 patients with SAB HLA antibodies, CPRA 10–99%, which also had a confirmatory LSPRA test, 95% (19) had one or more SAB false positive HLA antibodies. The number of false positive patient SAB antibodies ranged from 1 to 14, with a median of 3, MFI 900–3000. In 60% (12) of the patients, all of the SAB identified antibodies were all false positive, ranging from 1 to 14, with a median of 3. In 40% (8) of the patients, the LSPRA assay was able to confirm SAB HLA antibodies ranging from 1 to 20, with a median of 4. Conclusions It is unacceptable that alone, a SAB assay will result in about 3 false positive antibodies in 95% of patients who have HLA antibodies. The SAB assay is a very important test, but unless other testing platforms, like Phenotype beads and FlowPRA screen, are used to identify the false positive antibodies, the SAB assay will lose lifesaving organ offers for our patients or trigger unnecessary DSA treatments post transplant.