Which drug will not cause a positive direct antiglobulin test?

• A. Penicillin
• B. Aspirin
• C. Methyldopa
• D. Cephalexin

Answer: (B)

In drug-induced immune hemolytic anemia, a medication can trigger antibodies that bind to red blood cells in the circulation, so the direct antiglobulin test (DAT) becomes positive because it detects those antibodies or complement on the cell surface. Some drugs do this more readily: penicillin can act as a hapten and coat red cells with drug-dependent antibodies, cephalexin can also provoke antibodies that target the red cell surface, and methyldopa can induce autoantibodies against red cell antigens, all leading to a positive DAT.

Aspirin, on the other hand, is not typically associated with producing antibodies that coat red cells, so it usually does not cause a positive DAT.