Step 1 → Immunology Complement PathwaysPreview this topic sectionPreview the conditions. Plans unlock the full Step 1 details when you need them. Free Biochemistry Free Microbiology Plans Complement Pathways conditions Early Complement Deficiencies (C1–C4) Hereditary Angioedema (C1 Esterase Inhibitor Deficiency) Paroxysmal Nocturnal Hemoglobinuria (PNH) Terminal Complement Deficiencies (C5–C9)