Analytical validation of an ELISA-based test kit for polymeric IgA immune complexes in IgA nephropathy.

Abstract

Background and objectives: Circulating polymeric IgA immune complexes (Poly-IgA) have been proposed as potential biomarkers for IgA nephropathy (IgAN); however, standardized clinical assays for their detection are not yet available. We developed and analytically validated an ELISA-based test kit for Poly-IgA and evaluated its diagnostic performance in a retrospective, two-center cohort.

Materials and methods: Analytical validation of the ELISA kit was performed using samples collected from two independent centers. The validation included evaluation of the linear range, precision, and limit of detection (LOD). Clinical samples comprised healthy controls, patients with IgA nephropathy (IgAN), and patients with non-IgAN kidney diseases (nKD), including membranous nephropathy (MN), focal segmental glomerulosclerosis (FSGS), and other biopsy-confirmed glomerular diseases. Diagnostic sensitivity, specificity, and correlations with routine clinical parameters were evaluated.

Results: The test kit demonstrated robust analytical performance, with a limit of blank (LOB) of 10 U/mL, recovery ranging from 85 to 105%, and a linear range of 15.63 - 500 U/mL. Receiver operating characteristic (ROC) curve analysis of retrospective clinical samples yielded an area under the curve (AUC) of 0.87. At an optimal cutoff value of 75.6 U/mL, the assay demonstrated a sensitivity of 82.7%, specificity of 76.0%, and overall diagnostic accuracy of 78.0%. These findings suggest that the assay may serve as a promising diagnostic tool for differentiating IgAN from non-IgAN kidney diseases; however, further validation in larger, multicenter, and more diverse cohorts is warranted.

Conclusion: The ELISA-based Poly-IgA test kit was analytically validated and demonstrated good diagnostic performance in differentiating IgAN from nKD in a two-center cohort. Although its specificity of 76% is insufficient to replace kidney biopsy as the diagnostic gold standard, the assay may serve as a promising non-invasive adjunctive tool to support clinical decision-making, particularly for screening and disease monitoring. In light of these limitations, including the relatively small sample size, prospective multicenter studies in larger and more diverse populations are warranted to further establish its clinical utility.