I am interestingly following your discussion. If post transfusion sample shows a negative DAT and a mixed field reaction with anti Fya, indicating Free Fya cells in the circulation, there should be some other reason for gross icterus of plasma (otherthan the possible anti Fya mediated extra vascular haemolysis). The 1.8 degree Temperature rise at the end of transfusion should also have some other reason than possible anti Fya mediated immune haemolysis. Could be Febrile non haemolytic one or due to underlying condition/s.