LAUSR

The introduction of more sensitive and specific tools as solid phase immunoasssays has improved the ability to detect HLA antibodies. The techniques based on solid phase immunoassays in Luminex system can be performed either as screening assays (with pooled antigen panels that use bead populations coated in affinity-purified class I or class II HLA molecules) or to assess the specificity with single-antigen bead (SAB) assays (single cloned allelic HLA antigen).The sensitivity of each assay Is different, and their results may be discordant. Our objective was to evaluate the potential discrepancies between tests in a cohort of patients on our waiting list with no previous sensitizing events, for their potential influence in the access to transplantation. Observational study of 184 patients included in the kidney-transplant waiting list on March 31st, 2019. All possible sensitizing events (pregnancy, transfusion and previous transplants) were registered. HLA antibodies where analyzed both by screening and SAB tests. We limited the observations to males (64.7% of the cohort), as most women (95.4%) had a known sensitizing event, not being possible to discard possible pregnancies in the remaining. Of men, 46.2% had a sensitizing event and 63.8% did not. All 63 unsensitized patients showed a negative screening test, and 49 (77,78%) had at least one SAB done being positive in 73.4% (36/49). The positive SAB yielded a cPRA >10% in 30 cases (between 21-85%), mostly (27/30) due to HLA class II antibodies (88.8% with at least one DQ antibody) with a median MFI of 1571 (range:752-17650). A thorough review of specificities showed that 81% DQB1* and 89.6% DQA1* antibodies did not show consistency in all beads included for the same allele. Screening and SAB assays show a significant discordancy in unsensitized men included in the waiting list for kidney transplantation. Automated detection of antibodies by SAB without a proper specialized interpretation may wrongly limit access to transplantation.