Luminex screening first vs. direct single antigen bead assays: Different strategies for HLA antibody monitoring after kidney transplantation.

Luminex panel and single antigen beads (SAB) are used for screening and DSA specificity determination respectively. The cost of SAB may limit its general use, so some labs perform SAB tests only after positive screening. We compared both strategies: 1) SAB only if positive screening with kits from manufacturer A, and 2) direct SAB from manufacturer B, and correlate their sensitivity with histological findings. We selected 118 kidney transplant recipients with a normal biopsy (n = 19), histological antibody-mediated damage (ABMR, n = 52) or interstitial fibrosis/tubular atrophy (IFTA, n = 47) following Banff 2015 and 2017 classification. Direct SAB detected DSA in 13 patients missed by screening. Strategy 1 detected DSA in 0% normal, 61.5% ABMR and 8.5% IFTA patients; percentages with strategy 2 were 5.2%, 78.8% and 14.8% (p=0.004). Strategy 2 identified DSA allowing full ABMR diagnosis in 17% cases missed by strategy 1. Thereafter, direct SAB from manufacturer A confirmed DSA in 46% DSA-positive cases with strategy 2 (55.5% ABMR cases). Luminex screening failed to identify clinically relevant HLA antibodies, hampering DSA detection in patients with possible ABMR. Direct SAB testing should be the chosen strategy for post-transplantation monitoring, albeit direct SAB from the two existing manufacturers may diverge in as much as 50% of cases.

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