A transfusion reaction or event should always be part of a differential diagnosis if a patient has an immediate or post-transfusion change in symptoms or vital signs. Diagnosing a transfusion reaction during acute care, anesthesia, or surgery can be difficult due to multiple events occurring simultaneously. A febrile transfusion reaction is defined as an oral body temperature ≥38 °C (100.4 °F) and an increase in body temperature of ≥1 °C (1.8 °F) above pretransfusion baseline, or chills or rigors, during or up to 4 h after completion of a transfusion. It is appropriate to resume the same transfusion only in cases of a mild allergic transfusion reaction after patient evaluation and a positive response to management. All suspected transfusions should be reported to the hospital Transfusion Services (i.e., “blood bank”). Randomized controlled trials have yet to demonstrate a difference in transfusion reaction rates when patients are pretreated with acetaminophen or antihistamines.