Transfusion reactions are defined as adverse events associated with the transfusion of whole blood or one of its components. These may range in severity from minor to life-threatening. Reactions can occur during the transfusion (acute transfusion reactions) or days to weeks later (delayed transfusion reactions) and may be immunologic or non-immunologic. A reaction may be difficult to diagnose as it can present with non-specific, often overlapping symptoms. The most common signs and symptoms include fever, chills, urticaria (hives), and itching. Some symptoms resolve with little or no treatment. However, respiratory distress, high fever, hypotension (low blood pressure), and red urine (hemoglobinuria) can indicate a more serious reaction. Types of transfusion reactions include the following: acute hemolytic, delayed hemolytic, febrile non-hemolytic, anaphylactic, simple allergic, septic (bacterial contamination), transfusion-related acute lung injury (TRALI), and transfusion-associated circulatory overload (TACO). All suspected reactions should result in immediately stopping the transfusion and notifying the blood bank and treating clinician.