A direct antiglobulin test (DAT) positive result could indicate the presence of which on red blood cells?

A direct antiglobulin test (DAT) positive result could indicate the presence of which on red blood cells?

• A. IgG on red blood cells
• B. C3 on red blood cells
• C. None of the above
• D. Any of the above

Answer: (D)

Direct antiglobulin test detects immune components that are already bound to red blood cells in the patient. A positive result means there is something attached to the red cell surface that the antiglobulin reagent can recognize. That something can be IgG antibodies, or the complement protein C3, or both. Because either IgG or C3 (or both) on red blood cells will yield a positive DAT, any of those possibilities can cause a positive test. This underpins diagnoses such as autoimmune hemolytic anemia or transfusion reactions, where red cells are marked by antibodies or complement in vivo.

Direct antiglobulin test detects immune components that are already bound to red blood cells in the patient. A positive result means there is something attached to the red cell surface that the antiglobulin reagent can recognize. That something can be IgG antibodies, or the complement protein C3, or both. Because either IgG or C3 (or both) on red blood cells will yield a positive DAT, any of those possibilities can cause a positive test. This underpins diagnoses such as autoimmune hemolytic anemia or transfusion reactions, where red cells are marked by antibodies or complement in vivo.