Which organism is linked to cold agglutinin hemolytic anemia?

• A. Staphylococcus aureus
• B. Pseudomonas aeruginosa
• C. Mycoplasma
• D. Streptococcus pneumoniae

Answer: (C)

Cold agglutinin hemolytic anemia occurs when IgM antibodies bind red blood cells in the cold and activate the complement system, causing RBC destruction. The infection most classically linked to this process is Mycoplasma pneumoniae. In this setting, the immune response generates IgM antibodies that target RBC antigens; when blood cools in the extremities, these antibodies bind RBCs and trigger complement, leading to hemolysis and anemia, sometimes with acrocyanosis due to peripheral cooling. Because of this well-established association, Mycoplasma is the best choice for what organism is linked to cold agglutinin hemolytic anemia. The other organisms listed are not characteristically linked to this specific immune-mediated hemolysis.