Which of the following is a sign of a transfusion reaction?

Fever and chills are classic signs of a transfusion reaction. When a transfusion reaction occurs, the body responds to the foreign antigens introduced by the transfused blood. This immune response can manifest as an increase in body temperature (fever) as well as episodes of shivering or feeling cold (chills). These symptoms indicate that the immune system is actively responding to what it perceives as a threat, and they are often among the first symptoms noted when monitoring a patient's reaction to a blood transfusion.

In contrast, increased appetite, lower blood pressure, and labored sleep are not typically associated with transfusion reactions. Increased appetite does not reflect any physiological response to transfusion and does not relate to hemolysis or immune reaction. Low blood pressure can occur in severe transfusion reactions, but it is not as definitive as fever and chills. Labored sleep is not a recognized symptom associated with transfusion reactions, making it less relevant in this context.