Allergy tests may be of two general types. In vivo tests that measure the immune response to an agent called an allergen that induces an allergic (atopic) reaction, and in vitro tests that measure the antibodies that mediate an allergic response. Such antibodies are those of the immunoglobulin E class (IgE) which have epsilon heavy chains which attach to mast cells.
Allergy tests are performed to determine the cause of a person's allergic reaction. An allergic reaction is caused by the production of specific IgE antibodies against one or more antigens. Those antigens that elicit IgE production are termed allergens and are usually harmless substances.
Allergy related topics to be discussed on the next chapter are: