Autoimmune hemolytic anemia with a positive Coombs test and spherocytes on smear demonstrates which type of hypersensitivity?

• A. Type II hypersensitivity
• B. Type I hypersensitivity
• C. Type III hypersensitivity
• D. Type IV hypersensitivity

Answer: (A)

Antibody-mediated destruction of target cells. In autoimmune hemolytic anemia, autoantibodies bind to red blood cell surface antigens and activate complement, leading to destruction of the cells. The direct Coombs test detects these antibodies or complement on the RBC surface, giving a positive result, and the smear often shows spherocytes due to partial phagocytic removal of the red cell membrane by splenic macrophages. This combination—antibody binding to cell surface antigens with subsequent cytotoxic damage—is the hallmark of Type II hypersensitivity. Type I is IgE-mediated allergy, Type III involves immune complex deposition, and Type IV is T-cell–mediated delayed hypersensitivity.