Medical Laboratory Scientist (MLS) ASCP Practice Exam

In cases of mild allergic reactions to blood transfusions, plasma proteins are the most likely source of the allergen. During transfusions, the recipient may be sensitized to antigens present in the donor plasma, particularly immunoglobulins and other proteins. These can trigger an immune response leading to symptoms such as itching, hives, or urticaria.

Plasma contains various proteins, including antibodies and other molecules that can provoke an allergic response in susceptible individuals. This is especially the case in recipients who have been previously exposed to blood products or who have other allergies, as they may have IgE antibodies that react to these plasma proteins.

While red blood cells, white blood cells, and platelets can also be involved in transfusion reactions, they are more typically the culprits in hemolytic reactions or febrile non-hemolytic transfusion reactions rather than mild allergic reactions. Thus, plasma proteins are the key factor in initiating mild allergic responses during transfusions.