Optimizing HLA desensitization: serum dilution strategies and platform-specific MFI thresholds for antibody-mediated rejection risk in kidney transplantation.

Introduction: Highly sensitized kidney transplant (KT) candidates are at increased risk of antibody-mediated rejection (ABMR), particularly in the context of desensitization protocols. Accurate quantification of donor-specific antibodies (DSA) using Luminex single antigen bead (SAB) assays remains essential but is limited by signal saturation and inter-platform variability. Methods: We conducted a bicentric study involving 20 sensitized KT recipients undergoing HLA desensitization. Anti-HLA antibody profiles were analyzed using Immucor- Werfen (IM) and One Lambda-Thermofisher (OL) SAB platforms. Serum samples were tested both undiluted and at 1:10 dilution before and after desensitization. Results: Diluted pre-desensitization sera showed stronger correlation with post-desensitization DSA levels than pure sera (R² > 0.90 for IM; > 0.85 for OL). The sum of the DSA (sDSA) outperformed immunodominant DSA (iDSA) in predicting early ABMR. ROC analysis revealed good predictive power (AUC 0.79- 0.88), with IM providing superior iDSA discrimination. For the first time, we propose IM-specific MFI thresholds relevant for ABMR risk stratification. Discussion: Serum dilution improves the clinical interpretation of DSA intensity and refines risk assessment in desensitized KT candidates. Our findings support the integration of platform-specific MFI cutoffs and dilution-based antibody profiling into organ acceptance strategies for highly sensitized patients.