The RAST (Radioallergosorbent test), previously known as the "allergen-specific IgE blood test", is a laboratory test performed on blood. In a RAST test, a lab exposes a sample of the dog's blood to different test allergens such as animal dander, grasses, mites, or foods. Allergen-specific IgE antibodies (which are present if there is a "true" allergic reaction) will attach to a substance if the dog is allergic to it. A radioactive chemical is used in testing to help measure the results. The RAST test can be used to test for over 400 allergens.
The Phadebas RAST test from Pharmacia of Uppsala, Sweden, has for years been the gold standard for in vitro allergy testing. However, this first generation RAST test was not as sensitive as skin testing. The second generation Pharmacia ImmunoCap RAST has now almost completely replaced RAST tests throughout the world. It is a technically improved development of the original RAST, and the major advantage is that its sensitivity now approaches that of skin testing.