Assessing reference ranges for non-HLA antibodies: Comparative analysis of blood donors and kidney transplant candidates

BACKGROUND: The clinical relevance of non-HLA antibodies remains uncertain due to the lack of standardized assays. This study aimed to assess comparative reference values for non-HLA antibody profiles in a cohort of kidney transplant candidates on the deceased donor waiting list (WL group) with 0% calculated panel reactive antibodies (cPRA) and in healthy male blood donors (BD group). METHODS: Serum samples from 81 transplant candidates in the WL group and 92 individuals in the BD group were analyzed using the LABScreen™ Autoantibody Assay, which detects antibodies against 33 non-HLA antigens. Antibody positivity was defined using manufacturer-defined 95th percentile cut-off thresholds (COTs). Group comparisons were performed using non-parametric statistical methods, correlation analyses, and hierarchical clustering. RESULTS: Non-HLA antibody binding varied widely across antigens and cohorts. The BD group showed significantly higher median fluorescence intensity (MFI) values than the WL group for most antigens, except CXCL9 and GAPDH. Binding differences were observed between the BD and WL cohorts for most antigens, except for ARHGDIB (p = 0.565), NCL (p = 0.552), and GDNF (p = 0.08). Correlation analyses identified strong antigen pair associations (e.g., GDNF-REG3A, ρ = 0.83). Antibody reactivity against PRKCZ and CHAF1B differed significantly between cohorts, with higher reactivity observed in the BD group than in the WL group. CONCLUSIONS: This study demonstrates substantial heterogeneity in non-HLA antibody reactivity across antigens, with consistently lower antibody detection in the WL group. These findings support the concept that immune modulation in transplant candidates may reduce detectable non-HLA antibody levels and provide a rationale for defining reference cut-off values, particularly at the 95th percentile, for this population.