A 28-year-old man of Indian origin is admitted with acute hemolytic anemia (Hb 6.8 g/dL, reticulocyte count 8.2%, indirect bilirubin 4.2 mg/dL, LDH 1840 IU/L). Direct antiglobulin test (DAT/Coombs) is strongly positive with anti-IgG and anti-complement (C3) components. Blood film shows spherocytes and polychromasia. He denies recent transfusion, infection, or drug exposure. Serological workup reveals warm IgG antibodies reactive against all panel RBCs. What is the most appropriate next step in management?