Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal hematopoietic stem cell disorder caused by a somatic mutation in the PIG-A gene, which is essential for the biosynthesis of glycosylphosphatidylinositol (GPI) anchors that attach complement-regulatory proteins (CD55/DAF and CD59/MIRL) to the cell surface. Without GPI-anchored CD55 and CD59, red blood cells are unprotected from complement-mediated lysis, particularly during sleep when mild respiratory acidosis lowers blood pH and activates the alternative complement pathway, causing the characteristic morning hemoglobinuria (dark red-brown urine). Chronic intravascular hemolysis releases free hemoglobin that scavenges nitric oxide, causing smooth muscle dystonia (esophageal spasm, dysphagia, erectile dysfunction, abdominal pain), pulmonary hypertension, and a strongly prothrombotic state (hepatic vein thrombosis/Budd-Chiari syndrome is a classic complication). The nurse monitors urine color, serum LDH and haptoglobin as hemolysis markers, monitors renal function, monitors CBC for cytopenias (associated aplastic anemia), administers complement inhibitor therapy (eculizumab or ravulizumab -- anti-C5 monoclonal antibodies) as prescribed, ensures meningococcal vaccination before starting complement inhibitors, monitors for breakthrough hemolysis, manages iron and folate supplementation, and monitors for thrombotic complications.