What symptom is characteristic of an urticarial reaction to blood transfusion?

A urticarial reaction, commonly known as hives, is indeed characterized by the development of raised, itchy welts on the skin. This type of allergic reaction can occur during or shortly after a blood transfusion and affects the skin most prominently. The presence of hives signifies that the recipient's immune system is responding to certain proteins in the donor blood, leading to the release of histamines and subsequent skin manifestations.

Other symptoms associated with blood transfusion reactions can include hypotension, fever, or abdominal pain; however, these are indicative of different types of reactions. Hypotension can point to a more severe anaphylactic reaction or a hemolytic reaction rather than a urticarial response. Fever is typically associated with febrile non-hemolytic transfusion reactions, while abdominal pain may suggest a hemolytic reaction or infection, which again would not be consistent with a typical urticarial event. Thus, the clear and distinctive symptom associated with an urticarial reaction is the presence of hives.