The key question: Is it auto or allo ? This may be difficult to prove if the patient has been transfused.
If it is an autoantibody, I agree with Malcolm's position - who cares?
However, if the autocontrol is nonreactive, you may have to consider other things. Beware anti-Vel and anti-PP1pk (-Tja). These can behave like cold-reactive AUTO antibodies, i.e., demonstrate panagglutination, abolished reactivity by pre-warmed tests, etc.
There is at least one case (published by Jill Storry) of an anti-Vel that was "dismissed" as a cold auto (it was rendered nonreactive by pre-warming). The patient was transfused with random cells and had a fatal hemolytic reaction.