A Caution Against the Use of C5b-9 Endothelial Assay to Support Eculizumab Therapy: A response to Maritati et al.: “Eculizumab first” in the management of posttransplant thrombotic microangiopathy

In their recent study Maritati and colleagues reported 45 patients with early onset TMA after kidney transplantation.[1] Using serum of these patients an increased C5b-9 deposition on endothelial cells was observed in 84%. The authors suggest that these positive test results support the effective use of eculizumab. We caution against such conclusion. Initially, it was hoped that the ex-vivo complement assay would allow to evaluate the presence of factors in serum that augment complement activation on endothelial cells, and to identify patients with (risk of) TMA caused by complement dysregulation.