Proposed algorithm to cautiously explore and treat complement dysregulation in patients with TMA features presenting in emergency or intensive care units with a suspicion of atypical HUS. * Clinical and biological features including anti RNA polymerase 3 antibodies. Abbreviations: TMA, thrombotic microangiopathy; TTP, thrombotic thrombocytopenic purpura; STEC HUS, shiga-toxin Escherichia coli hemolytic uremic syndrome; MMACHC, cobalamin C-related HUS; HUS, hemolytic uremic syndrome; SoC, standard of care; APL, anti-phospholipid. Inspired from Timmermans et al., J. Clin. Med., 2021 [5], Fakhouri et al., Nat. Rev. Nephrol., 2021 [55] and Nester et al., Mol. Immunol., 2015 [66].