Allergy skin tests are currently performed percutaneously using a variety of skin-prick tools, in order to detect allergies responsible for "atopy", including seasonal allergic rhinitis or rhino-conjunctivitis (also known as hay-fever or pollenosis) or perennial rhinitis (occurring year-round), recurrent sinusitis, chronic sinusitis, recurrent upper respiratory tract infections (especially in children), allergic asthma, certain forms of urticaria (hives), and sometimes to investigate a skin reaction called dermatitis, including atopic dermatitis or eczema.
Allergy extract trays
Available skin-prick tools
The tests are performed to detect several environmental allergens, including dust mites, feathers, moulds, pollens, animal allergens, in addition to related food allergies. The tests can also be performed to detect the venom of certain insects (bees, wasp, hornets, etc), local anaesthetics, and latex.
Placement of extracts
Skin-prick testing through the extracts
The only medication that can be tested by routine skin testing is penicillin. The tests are performed by pricking the skin, using a variety of tools, needles or lancets. Intradermal testing (by small injection) can be performed if skin-prick testing is negative. The results are read in 15-20 minutes, and are described in terms of mild, moderate, or marked, as a series of 'pluses' (such as +, ++, +++, or ++++) or by measuring the induration, and the erythema in mm.
A test by intradermal injection
A case example: reading after 15 minutes
A test after applying ice
Allergists can also evaluate allergies by ordering certain blood tests (formerly called RAST, or radioallergosorbent tests) which give a quantitative level of IgE antibodies responsible for allergic manifestatins. They can be performed for most environmental allergens, foods and venoms, particularly if the skin-prick tests are difficult or impossible to perform; in the case of important skin rashes which prevent testing, or occasionally in significant food hypersensitivity. Recently the specific IgE antibody test has improved considerably and is now available under the CAP system (Pharmacia-Upjohn) – its capacity to detect allergic sensitivity is greater than 95%.
Local application of allergy skin tests ("patch tests") are performed in cases of contact dermatitis. The extract is applied to the skin, covered in a special tape, and readings are performed after 24 hrs or longer. This kind of allergy is called "delayed", different from allergies known as "atopic" (such as pollens and animals, etc) which are usually immediate, and is frequently performed by dermatologists in addition to allergists, in order to detect skin sensitivities to certain cosmetics, jewellery, and perfume among other chemicals.
Local application of heat or cold, often performed with ice, can also be a form of allergy testing. The photo shows a test performed with an ice cube on the forearm. The test is positive, seen by the presence of a "hive" in the region of the ice, after application for one minute.