Validation and performance of MicroVue sC5b-9 Plus ELISA on the Dynex DS2 platform

Background: The complement membrane attack complex involves C5b-mediated assembly of C6-C9 polymers to form pores in cell membranes during complement activation. Inactive complexes can become soluble C5b-9 (sC5b-9) when they bind to Protein S. Elevated sC5b-9 levels are associated with increased risk of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), a serious condition which can be improved with eculizumab therapy. Early detection of TA-TMA is essential for improving patient outcomes and optimizing the use of this costly treatment. We assessed the Quidel Microvue sC5b-9 Plus Enzyme Immunoassay on the Dynex-DS2 platform to screen for patients at risk of TA-TMA. Methods: EDTA plasma samples were collected from bone marrow transplant (BMT) patients and others not at risk for TA-TMA. Assay validation included correlation with another laboratory, precision, linearity, and hemolysis interference. Additionally, clinical accuracy was assessed through retrospective patient data analyses. Results: The assay showed acceptable intra- and interday precision, with less than 13 % variation. Linearity ranged from 80 to 1600 ng/mL, and there was no hemolysis interference up to 800 mg/dL. Clinical data revealed that monitoring sC5b-9 levels could detect significant increases indicative of TA-TMA, facilitating timely eculizumab intervention. Analytically, changes in sC5b-9 by 2- to 3-fold were significant for patient monitoring of TA-TMA. Lastly, a retrospective analysis on utility of the assay demonstrated effective utilization at our institution. Conclusion: The Quidel Microvue sC5b-9 Plus Enzyme Immunoassay demonstrated good analytical and clinical performance in screening patients with increased risk of TA-TMA.