Which finding indicates an allergic reaction during a blood transfusion?

Uticaria, or hives, is a classic sign of an allergic reaction during a blood transfusion. This condition is characterized by raised, itchy welts on the skin, which result from the body’s immune response to an allergen. In the case of a blood transfusion, the allergen could be proteins in the donor blood that provoke an immune response in the recipient.

Allergic reactions can vary in severity, and typically, they manifest within minutes of exposure to the blood products. The presence of hives indicates the body is reacting to the transfused blood, often due to the presence of foreign proteins that the recipient’s immune system identifies as harmful.

Other findings, such as increased heart rate, hypotension, and fever, can occur during transfusions but are more indicative of other types of reactions. Increased heart rate can result from various stress responses or anemia, hypotension may signal fluid overload or other complications, and fever might suggest an infection or a febrile non-hemolytic reaction rather than a direct allergic response. Thus, uticaria specifically highlights an allergic reaction, making it the key indicator in this scenario.