Study design. Patients enrolled in the OLE study who experienced an acute BTH event had the opportunity to receive either intensive subcutaneous or intravenous pegcetacoplan as an acute treatment for BTH. Patients who experienced an acute BTH event but had chosen not to receive intensive pegcetacoplan could continue to participate in the OLE study with the potential to receive a dose adjustment to 1080 mg every third day or 3 times weekly. BTH, breakthrough hemolysis; LDH, lactate dehydrogenase; PEG, pegcetacoplan; Q3D, every 3 days; SC, subcutaneous; TIW, 3 times weekly; ULN, upper limit of normal.