In direct antiglobulin testing, what does detection of C3d on red cells suggest?

In direct antiglobulin testing, what does detection of C3d on red cells suggest?

• A. Complement-mediated hemolysis is possible
• B. Autoantibody not involved
• C. Cold agglutinin disease only
• D. HIV infection

Answer: (A)

Direct antiglobulin testing detects antibodies or complement components bound to red cells in the patient. If C3d is found on the red cells, it means the complement system has been activated and deposited on the cell surface. That makes complement-mediated hemolysis a real possibility because the immune attack can proceed through the complement cascade, leading to red cell destruction. This finding does not exclude the involvement of antibodies—autoantibodies can be present and still trigger complement. It also isn’t limited to cold agglutinin disease; several autoimmune hemolytic processes can involve complement deposition. HIV infection isn’t indicated by the presence of C3d alone, which is why the most accurate takeaway is that complement-mediated hemolysis is possible.

Direct antiglobulin testing detects antibodies or complement components bound to red cells in the patient. If C3d is found on the red cells, it means the complement system has been activated and deposited on the cell surface. That makes complement-mediated hemolysis a real possibility because the immune attack can proceed through the complement cascade, leading to red cell destruction.

This finding does not exclude the involvement of antibodies—autoantibodies can be present and still trigger complement. It also isn’t limited to cold agglutinin disease; several autoimmune hemolytic processes can involve complement deposition. HIV infection isn’t indicated by the presence of C3d alone, which is why the most accurate takeaway is that complement-mediated hemolysis is possible.