A-330 Trending Treatment of Transplant-associated Thrombotic Microangiopathy (TA-TMA): Validation and Performance of Soluble C5b-9 on the Dynex DS2 Platform

Abstract

Abstract Background The complement system membrane attack complex is comprised of the C5b fragment along with C6, C7, C8 and C9 polymers that form a pore to disrupt a membrane during complement activation. Inactive complexes that are not membrane-bound combine with Protein S to form soluble C5b-9 (sC5b-9). Elevated concentrations of sC5b-9 are associated with risk of development of hematopoietic stem cell transplant-associated thrombotic microangiopathy (TA-TMA), which can be treated by eculizumab therapy. TA-TMA is a complex syndrome of abnormal cell activation, microvascular hemolytic anemia, and complement dysregulation which can lead to multiple organ dysfunction and death. Therefore, recognition of this syndrome is critical in the context of not only preventing poor outcomes in patients but also promoting stewardship of an expensive, yet effective therapy. Our laboratory evaluated the performance of the Quidel Microvue sC5b-9 Plus enzyme immunoassay on the Dynex-DS2 platform for clinical use. Methods EDTA plasma samples were collected from remnant CBC samples ordered for bone marrow transplant (BMT) patients and other patients not at risk for TA-TMA. Validation studies included method correlation, inter- and intraday precision, assay linearity, hemolysis interference, and other experiments. Clinical accuracy was assessed by performing a retrospective review of sC5b-9 results from BMT pediatric patients at risk for TA-TMA. Results Intraday precision was 6.7%, 7.1% for the manufacturer low- and high-quality control materials, respectively and 9.9% for an in-house prepared plasma pool. Inter-day precision was 9.8% and 5.3% for manufacturer low- and high-quality control material, and 12.8% for an in-house plasma pool over a period of at least five days. The linearity of the assay was verified with a lower limit of quantification of 80 ng/mL and upper limit of qualification of 1600 ng/mL. Our method comparison indicated good correlation with send-out results, with an average percent bias of -10% and Pearson's r2 value of 0.986. The assay showed no interference up to 100 mg/dL of hemolysis. Retrospective analysis of a few patient results demonstrated that weekly monitoring of sC5b-9 concentrations detected rapid increases in patients at risk of TA-TMA, which prompted treatment with eculizumab therapy. Given the analytical performance, at least 2- to 3-fold changes in sC5b-9 concentrations are clinically meaningful when tracking trends in patients at risk for TA-TMA. Conclusion Our results indicate the Quidel Microvue sC5b-9 Plus enzyme immunoassay on the Dynex-DS2 platform had acceptable analytical and clinical performance for monitoring trends in patients at risk for TA-TMA.