Analytic Performance of MicroVue Enzyme Immunoassay (EIA) for Measurement of Ba and sC5b-9 for Urine

Background: Complement mediated kidney diseases, including C3 glomerulopathy (C3G), atypical hemolytic uremic syndrome (aHUS), lupus nephritis (LN), and immunoglobulin A nephropathy (IgAN) are chronic inflammatory conditions characterized by dysregulated complement activation. Traditionally, complement activation is measured in plasma. However, patients with kidney disease often have an abundance of complement activation fragments in their urine – including Ba and soluble C5b-9 (sC5b-9), markers of alternative pathway activation and terminal pathway activation respectively– highlighting the potential value of Ba and sC5b-9 measurement in urine for diagnosis and risk management in patients with C3G, aHUS, LN, IgAN, and other kidney diseases. Herein we evaluated the analytical performance of the Quidel MicroVue Plus EIA Ba and sC5b-9 for urine samples. Methods: The Quidel MicroVue Ba and sC5b-9 Plus EIA were evaluated using randomly collected healthy urine samples or healthy urine samples spiked with a known concentrations of Ba and sC5b-9, as well as chronic kidney disease (CKD) urine samples. Results: The analytical performance of the assays met acceptability criteria for accuracy and precision. Assay accuracy was (100 ± 20%) and intra-assay precision as well as inter-assay precision was ≤ 20 % coefficient of variability (CV) for both assays. Ba was detected in healthy urine samples (N=40), but sC5b9 was not. Positive linearity was observed in both assays over a wide range of concentrations. Ba and sC5b-9 measured in urine was stable following three freeze-thaw cycles. Lastly, Ba and sC5b-9 measured in urine was stable when stored at -20°C and -80°C for 4 weeks. Long term stability testing at -80°C is underway. Conclusion: Quidel MicroVue Ba and sC5b-9 Plus EIA are accurate, and reliable assays for detection of Ba and sC5b-9 in urine samples, making it a viable alternatibe to plasma.