Atypical hemolytic uremic syndrome (aHUS) is a complementmediated thrombotic microangiopathy (TMA) characterized by mechanical hemolysis, renal impairment, thrombocytopenia, and preserved ADAM metallopeptidase with thrombospondin type 1 motif 13 (ADAMTS13) function. 1, 2 Historically, patients with aHUS had poor outcomes, with 5-year end-stage renal disease-free survival of only 36%. 3 The use of eculizumab, a monoclonal antibody against the terminal complement component C5, results in improvements in thrombocytopenia, hemolysis, and renal function. 4, 5 The necessary duration of eculizumab treatment in aHUS is unknown. Before aHUS was distinguished from thrombotic thrombocytopenic purpura, both were treated with plasma therapy, and treatment duration was determined by clinical response. 6-8 Emerging evidence suggests aHUS may not require indefinite eculizumab treatment, and cessation may help mitigate sequelae of therapy. 9-11 Although the risk for meningococcal infection in immunized patients is low, eculizumab costs $7,696.80/300 mg at our institution, or $800467 for yearly maintenance; this is in agreement with reports of $723 520 per year by average wholesale price, accounting for the doses used in aHUS. 4, 12, 13 The costs and logistical barriers of prolonged treatment are substantial in resource-rich nations, whereas in other nations, this therapy may not be available because of cost. 12, 14, 15 We examined our institutional experience on eculizumab cessation in adult aHUS to determine benefits and outcomes associated with therapy cessation. In accordance with institutional review board–approved protocols, adult patients were identified from the Johns Hopkins Complement Associated Disease registry for this single-center, retrospective review. 16 Patients were included if they fulfilled aHUS criteria, had negative testing for Shiga toxin when applicable, had ADAMTS13 levels above 10%, and received eculizumab at the discretion of the treating physicians. We report dialysis independence at last follow-up, TMA-event-free status as in Legendre et al, 5 and relapse as in Fakhouri et al. 10 Detailed methods are reported in the supplemental Appendix, available on the Blood website.

Seventeen patients were treated with eculizumab (Table 1). Patient 14 experienced a prior episode of aHUS at age 7 years and was in remission for 44 years before the event reported here. Median patient age at presentation was 46 years, 76% were female, and 70% were white. Median ADAMTS13 activity was 60%(range, 15%-102%), and admission hemoglobin was 8.3 g/dL (range, 3.3-13.3). Plasma exchange was initiated before eculizumab in 64% of patients, and all patients began eculizumab with active aHUS. Median duration of eculizumab therapy was 90.5 days before physician-directed cessation (range, 14-545 days), and postcessation follow-up was median 308.5 days (range, 33-1390 days). There were no episodes of meningococcal infection. One patient developed bacteremia from an indwelling infusion catheter and was hospitalized. Two patient deaths occurred. Patient 16 died on eculizumab therapy; infected vascular access was suspected, with nonadherence concerns. Patient 17 had eculizumab