(RAST), is the name given to an in vitro technique which detects the presence of IgE (and IgG) antibodies to allergens, proteins which may give rise to hypersensitivity reactions seen in allergies. Allergens are coated on a complex carbohydrate matrix called a sorbent. Antibodies specific for the allergen being tested bind to the allergin and, if preset, are detected by a low-level radioactively labeled antibody to either human IgE or IgG, depending upon the isotype being used.