1) Blood transfusion is generally safe but risks include acute haemolytic transfusion reactions, transfusion-related acute lung injury, allergic reactions, and bacterial contamination. 
2) If a transfusion reaction is suspected, the transfusion must be stopped immediately and the patient closely monitored and treated depending on symptoms.  
3) Investigations include blood and urine samples, and the transfusion reaction report form must be completed to document the event and aid investigation.