What is the most likely cause of a positive DAT and hemoglobinemia after blood transfusion in a patient with a known anti-Fya?

A positive direct antiglobulin test (DAT) along with hemoglobinemia following blood transfusion indicates that there has been some degree of hemolysis. In the context of a patient with a known anti-Fya antibody, this situation suggests that the hemolysis is likely immune-mediated.

A febrile non-hemolytic reaction is characterized primarily by fever and chills occurring during or shortly after a transfusion, usually without hemolysis. Therefore, in this case of having hemoglobinemia and a positive DAT, identifying this reaction as the cause would not logically fit since it typically does not result in red blood cell destruction.

An acute hemolytic reaction occurs if a patient receives incompatible blood, which leads to immediate destruction of transfused red blood cells, often with severe symptoms such as fever, chills, back pain, and hemoglobinemia. While anti-Fya could mediate such a reaction, this would generally present more dramatically and is typically connected with ABO incompatibility or other significant alloantibodies.

A delayed hemolytic reaction usually manifests days to weeks after transfusion, where a previously sensitized patient develops hemolysis due to a secondary response to an antigen present on the transfused red blood cells. In