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Cold agglutinin disease(CAD) is an uncommon form of autoimmune hemolytic anemia characterized by cold-reacting IgM autoantibodies that bind to erythrocyte surface antigens at temperatures below 30°C, leading to agglutination and complement-mediated hemolysis. It may occur as a primary (idiopathic) disorder, most often in adults over 50, or secondary to infections (e.g., Mycoplasma pneumoniae, Epstein–Barr virus), lymphoproliferative diseases, or other autoimmune conditions.

 Clinical features reflect both anemia and impaired microcirculation. Patients commonly report fatigue, weakness, pallor, dizziness, and dyspnea; hemolysis may cause jaundice and dark urine. Cold exposure precipitates acrocyanosis or Raynaud-like phenomena—painful, purplish discoloration of fingers, toes, ears, and nose—and can worsen symptoms in winter. Severe cases may present with tachycardia, chest pain, or signs of cardiac strain due to increased workload from chronic anemia.

Diagnosis relies on demonstrating cold agglutinins, elevated markers of hemolysis (e.g., LDH, indirect bilirubin, low haptoglobin), and a positive direct antiglobulin test (typically complement C3). Management emphasizes strict cold avoidance, treating underlying causes, and supportive care such as warmed red cell transfusions in acute severe anemia. Pharmacologic options include rituximab-based regimens and the complement inhibitor sutimlimab to reduce hemolysis and transfusion requirements.