Just a thought but why must the acute pain be associated with the transfusion? Why was the patient being transfused, trauma, chronic anemia, etc.? It makes a difference. Where was the pain, at the site the blood was going in, along the same vein, some other part of the body? I know that it is a natural reaction for us to associate anything unexpected which occurs during or shortly after a transfusion to associate it with the transfusion but that is not always the case. It is worth the effort to also look elsewhere for the cause. As I've mentioned in other threads, I've seen a temp rise post transfusion that was caused by the window blinds being open and the sun shining directly on the patient. Bottom line is that it is not always the transfusion causing what you are seeing. Keep an open mind.