BackgroundAtypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy (TMA) characterized by platelet consumption, hemolysis, and organ damage. Eculizumab (ECU), a humanized antibody that blocks complement activity, has been successfully used in aHUS, but the best treatment schedule is not yet clear.MethodsHere, we report our experience with ECU maintenance treatment and the interval between subsequent doses being extended based on global classical complement pathway (CCP) activity aimed at <30% for maintaining aHUS into remission.ResultsWe report on 38 patients with aHUS, 13 children, 21 female, with a median age of 25.0 years (range 0.5–60) at disease onset treated with ECU standard schedule for a median of 2.6 months (range 0.4–24.6). Once stable TMA remission was obtained, the interval between ECU doses was extended based on complement function, with a target CCP activity of <30%. With this approach, 22 patients regularly receive ECU infusion every 28 days and 16 every 21. During a median observation period on ECU, an extended interval of 26.9 months (range 0.8–80.9), with a cumulative observation period of 1,208 months, none of the patients relapsed.ConclusionMonitoring complement activity allows a safe reduction in the frequency of ECU administration in aHUS while keeping the disease in remission.