Allergies Health Article

When to call the doctor

Parents should consult a physician when a child has repeated and prolonged symptoms. Allergic rhinitis may be mistaken for a cold or other upper respiratory infection. Usually, a fever indicates an infection. Food allergies and allergies to insect stings or medications can be especially dangerous, causing anaphylactic reactions that require emergency treatment.

Diagnosis

Allergies can often be diagnosed by a careful medical history, matching the onset of symptoms to the exposure to possible allergens. Allergy is suspected if the symptoms presented are characteristic of an allergic reaction, and this occurs repeatedly upon exposure to the suspected allergen. Allergy tests can also be conducted to determine allergens.

Skin tests

Skin tests are performed by administering a tiny dose of the suspected allergen by pricking, scratching, puncturing, or injecting the skin. The allergen is applied to the skin as an aqueous extract, usually on the back, forearms, or top of the thighs. Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare). The tests usually begin with prick tests or patch tests that expose the skin to small amounts of allergen to observe the response. A positive reaction occurs on the skin even if the allergen is at levels normally encountered in food or in the airways. Reactions are usually evaluated approximately 15 minutes after exposure. Intradermal skin tests involve injection of the allergen into the dermis of the skin. These tests are more sensitive and are used for allergies associated with risk of death, such as allergies to antibiotics. Skin testing may be painful for children.

Provocation tests

These tests involve the administration of allergen to elicit an immune response. Provocation tests, most commonly done with airborne allergens, present the allergen directly through the route normally involved. Delayed

allergic contact dermatitis diagnosis involves similar methods by application of a skin patch with allergen to induce an allergic skin reaction. Food allergen provocation tests require abstinence from the suspect allergen for two weeks or more, followed by ingestion of a measured amount of the test substance administered as an opaque capsule along with a placebo control. Provocation tests are not used if anaphylaxis is a concern given the patient's medical history.