Which of the following would yield a positive direct antiglobulin test (DAT)?

Which of the following would yield a positive direct antiglobulin test (DAT)?

• A. Presence of IgG on red blood cells
• B. Presence of C3b or C3d on red blood cells
• C. A transfusion reaction caused by preformed antibody
• D. Any of the above

Answer: (D)

Direct antiglobulin test detects antibodies or complement bound to red blood cells in the patient. If IgG is attached to red cells, the DAT is positive. If complement components such as C3b or C3d are deposited on red cells, the DAT is positive as well. A transfusion reaction caused by preformed antibodies against donor antigens also results in antibodies (and often complement) coating the transfused cells, yielding a positive DAT. Because all of these involve in vivo sensitization of red cells with antibody or complement, the test can be positive in any of these scenarios. Any of the above can yield a positive DAT.

Direct antiglobulin test detects antibodies or complement bound to red blood cells in the patient. If IgG is attached to red cells, the DAT is positive. If complement components such as C3b or C3d are deposited on red cells, the DAT is positive as well. A transfusion reaction caused by preformed antibodies against donor antigens also results in antibodies (and often complement) coating the transfused cells, yielding a positive DAT. Because all of these involve in vivo sensitization of red cells with antibody or complement, the test can be positive in any of these scenarios. Any of the above can yield a positive DAT.