A 68-year-old male with a history of myelodysplastic syndrome receives a transfusion of 2 units of packed red blood cells.
Five days later, he presents with a low-grade fever, mild jaundice, and a greater than expected drop in his hemoglobin level.
A direct antiglobulin test (DAT) is now positive.
Which of the following is the most likely cause of this presentation?
