A comprehensive comparative assessment of mean fluorescence intensity of luminex single antigen bead tests between laboratories and commercial platforms: A report from the Italian Histocompatibility Network.

Reliable and reproducible testing of Donor Specific HLA-Antibodies (DSA) is essential for clinical decisions in organ transplantation. In this prospective multicentre study from the Italian Transplant Network, we assessed reproducibility and possible bias of Mean Fluorescence Intensity (MFI) values of Luminex-Single Antigen Bead (SAB) assays across 20 laboratories using the 2 commercially available platforms (Vendor 1 and Vendor 2). Both Vendors showed inter-laboratory median MFI coefficient of variation below 20 %. We evaluated the possible MFI bias between Vendors. In the clinically significant 1000-10000 MFI range, a strong MFI bias was observed for class I SAB, with Vendor 1 MFI being approximately one third of Vendor 2 (Vendor 1 MFI = 0.36 Vendor 2 MFI). For class II, the MFI bias was lower, approximately three quarters of Vendor 2 (Vendor 1 MFI = 0.74 Vendor 2 MFI), with several discrepant results for DQ alleles. Ultimately, we defined the best fitting cutoff values for positive and permissive DSA (1000 and 3000, respectively) in use in the current Italian National Kidney Allocation System. These were 500/1000 and 500/2000 for class I and class II for Vendor 1 compared to 1000/3000 for both classes in Vendor 2. Overall, we developed a tool to compare MFI values between different platforms for consistent DSA assignment across laboratories and enable the most appropriate clinical decisions in organ transplantation.