Résumé
Background Although terminal complement inhibitors transformed the prognosis of atypical haemolytic uraemic syndrome (aHUS) from dismal to favourable, treatment approaches vary due to the intermittent disease nature and high costs. Occasionally, complement inhibition is applied in infectious (i)HUS. We aimed to examine real-world C5 inhibitor use and its impact on patient outcomes. Methods This retrospective cohort study used longitudinal data from the European Rare Kidney Disease Registry, collected from 76 nephrology centres across 24 European countries between January 1, 2019 and January 31, 2024. Eligible patients had aHUS or iHUS with onset after January 1, 2011, and/or documented C5 inhibitor use. Exclusions included complement-unrelated HUS, post-transplant HUS, and prophylactic C5 inhibitor use around kidney transplantation. Data, derived from medical records and focused queries, were used to assess C5 inhibitor duration, via time-to-event analysis, and kidney function based on annual creatinine levels. Findings A total of 238 aHUS and 472 patients with iHUS were included in the analysis. C5 inhibition was applied in 76.5% of aHUS and 18.4% of iHUS, with major utilisation differences between countries (p < 0.0001) and less common use in female patients with aHUS (p = 0.0022). Median (interquartile range) treatment duration was 16.1 (3.6-41.2) months in aHUS and 9 (7-32) days in iHUS. After five years, 56% of genetic, 28% of anti-complement factor H (anti-CFH) antibody-mediated, and 23% of aHUS cases with no identified cause remained on treatment. The long-term (>7 years) risk of treatment resumption was 35% in genetic, 15% in aHUS of no identified cause, and 0% in anti-CFH antibody-mediated aHUS. Post-withdrawal aHUS relapses were mostly mild and did not lead to permanent kidney function impairment, ultimately leading to long-term treatment withdrawal in 92.5% of discontinued cases. Interpretation Currently, C5 inhibitors are administered in three-quarters of newly diagnosed patients with aHUS in Europe, with varied utilisation and discontinuation practices. Treatment withdrawal is common and safe, although relapses may occur, particularly in genetic aHUS. However, baseline disease severity, selective use in expert centres, and indication bias affect outcome comparability. Findings must be considered in the context of patient- specific factors and disease severity at the time of treatment decisions. Copyright (c) 2025 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).