Single antigen (SA) tests are indispensable for an accurate HLA antibody identification in sera of transplant patients. Three commercial tests using purified single antigens combined with microbead or microarray technology are currently available. This study aims to determine the prognostic value of these tests prior to kidney transplantation. Forty-nine pretransplant sera with donor-specific antibodies (DSA) from patients who underwent kidney transplantation from a living donor were selected from a previous multicentre study. All sera were tested by a new microspot SA test from BAG and bead array SA assays from Immucor/Werfen (IMM) and One Lambda/ThermoFisher (OLI). AMR-free survival within 6 months (AMR-S) and 10-year death-censored graft survival (10yGS) were compared to DSA-negative patients from the original study and evaluated according to (1) number of SA tests classifying the serum as DSA-positive (DSA+), and (2) number of SA tests detecting at least one identical DSA specificity. In part (1), the 22 patients classified as DSA-positive by all tests had lowest AMR-S and 10yGS. OLI was most sensitive and classified all sera as DSA-positive that were DSA-positive by BAG and/or IMM. However, the 14 patients who were DSA-negative by both BAG and IMM, had similar AMR-S and 10yGS like patients without any DSA. Overall, BAG and IMM had comparable sensitivities. In part (2), at least one identical DSA was detected by all tests in 18 patients, who had worse AMR-S and 10yGS. In 14 patients, the same DSA was detected by IMM and OLI, or by BAG and OLI, respectively. These patients had lower AMR-S, but no significant difference in 10yGS. In 17 sera, DSA were detectable by one or more tests, but no specificity was positive in more than one assay (in all sera DSA were detected by OLI, in one additionally another DSA by IMM and in two another DSA by BAG). AMR-S and 10yGS were similar to DSA-negative patients. Overall, all three SA assays were suitable for the reliable detection of strong DSA. OLI was shown to be the most sensitive assay, but also prone to possible false positive results defined by the lack of an association with impaired outcomes. Future studies are needed to determine how many OLI-only reactions are caused by very weak DSA and how many by reactions with denatured beads. While such reactions were rare for BAG and IMM assays, these tests missed some DSA associated with an increased risk for AMR.
Heinemann et al. (Wed,) studied this question.