A-140 Analytical and clinical validation of the quidel microvue sc5B-9 enzyme immunoassay in a pediatric population

Abstract Background The complement system plays a key role of surveillance for the immune system and its dysregulation has been implicated in different diseases. Soluble C5b-9 (sC5b-9) is a soluble form of the Terminal Complement Complex (TCC) that is released into the circulation with elevated levels associated with increased risk in patients with atypical uremic syndrome (aHUS) and other chronic inflammatory conditions. With the advent of eculizumab, a complement c5 inhibitor, proper testing for diagnoses and therapeutic monitoring are warranted. Also, sC5b-9 levels could increase during extracorporeal membrane oxygenation (ECMO) and serve as an early indicator of thrombotic microangiopathy (TMA). Methods We evaluated both the analytical and clinical performance of the Quidel Microvue sC5b-9 Plus enzyme immunoassay. Analytical performance was evaluated with precision (intra- and inter-assay), linearity, interference studies and correlation with a reference laboratory. Reference intervals was established using plasma samples from control donors. Clinical performance of the assay was assessed using EDTA-anticoagulated plasma of patients who are on extracorporeal membrane oxygenation (ECMO) who have acquired von-Willebrand disease and patients with reduced ADAMTS13 activity. Results The assay showed acceptable intra and inter-precision with a CV of less than 16% for both low and high levels. Linearity ranged from 12.6 to 160.66 ng/ml, while accuracy and method correlation studies with a reference laboratory yielded a correlation coefficient (R) of 0.96. Dilution studies revealed a clinical reportable range extending to 2560 ng/mL. Hemolysis, icterus and lipemia did not affect the assay at 500 mg/dl, 40 mg/dl and 1000 mg/dl respectively. Reference range in control donors was established at = 268.0 ng/mL (range from 128.0 to 268.0 ng/mL). Clinical performance of the assay in patients with low ADAMTS13 activity and acquired von-Willebrand disease (AVWS) revealed elevated sC5b-9 levels of 2241.5 ± 983 ng/mL and 1575.5 ± 756 ng/mL respectively suggesting complement activation in these patient cohorts compared with controls with sC5b-9 levels of 196.3 ± 37.4 ng/mL. Conclusion The Quidel Microvue sC5b-9 plus EIA assay demonstrated acceptable analytical performance and clinical utility for monitoring complement activation in patients. Further studies will be done to correlate sC5b-9 levels with existing markers of complement activation.