In the case of a positive DAT, what could indicate a previous sensitization to a transfusion-related antigen?

A positive Direct Antiglobulin Test (DAT) indicates the presence of antibodies bound to the surface of red blood cells, suggesting that there has been a prior immunological response. In the context of transfusion-related antigen sensitization, a prior transfusion with negative antibody screens could suggest that the patient has been exposed to a transfusion-related antigen that was not detected in an earlier screening. This exposure may lead to the development of antibodies against that specific antigen.

Similarly, having had a recent pregnancy can also indicate previous sensitization because pregnancy can expose a person to fetal red blood cells that express paternal antigens, which may be foreign and elicit an immune response similar to that seen in transfusion reactions.

Since both a prior transfusion and a recent pregnancy can result in sensitization to blood group antigens and subsequently lead to a positive DAT, both scenarios are relevant in explaining the test result. This is why the correct answer combines both options, acknowledging that both previous transfusion and recent pregnancy can be sources of exposure that lead to the formation of antibodies detectable by the DAT.