Allergies and Hypersensitivities - Diagnosis of allergies

Some allergic reactions are outgrown; some don't develop until adulthood; some become increasingly severe over the years because each repeated exposure makes the body more sensitive to the allergen. In many instances, the irritating substance is easily identified, after which it can be avoided. In other cases, it may take a long series of tests before the offending allergen is tracked down.

Medical History

If a person suspects he may have an allergy, the first thing he should do is consult a physician to see if the help of an allergy specialist should be sought. The physician or allergist will first take a complete medical history and check the patient's general health. Not infrequently the source of an allergy can be found by general questioning about the patient's life style. For example, the reaction may occur only on or immediately after the patient eats seafood. Or a patient may have an apparently chronic allergy but be unaware that it may be related to daily meals that include milk and eggs. A patient who keeps several cats or sleeps every night with a dog in the bedroom may not realize that an asthmatic condition actually is an allergic reaction to dander from the fur of a pet animal.

The history taken by the physician will include questions about other known allergies, allergies suffered by other members of the family, variations in symptoms according to the weather, time of day, and season of the year. The symptoms may be related to a change in working conditions or the fact that the symptoms, if perhaps a result of house dust, diminish during periods of outdoor exercise. A person sensitive to cold may unwittingly exacerbate the symptoms with cold drinks, while another person who is sensitive to heat may not realize that symptoms can be triggered by hot drinks but relieved by cold drinks, and so on.

Skin Testing

If the patient is referred to an allergy specialist, the allergist will continue the detective story by conducting skin tests.

Scratch Test

Based on information in the medical history of the patient and the allergist's knowledge of molds, pollens, and other airborne allergens in the geographical area, “the allergist” will conduct what is called a scratch test .

A diluted amount of a suspected allergen is applied to a small scratch on the patient's arm or back. If the results of the scratch test are inconclusive, a more sensitive test may be tried.

Intracutaneous Test

In the intracutaneous test, a solution of the suspected allergen is injected into the underlayer of skin called the dermis . The intracutaneous test also may be used to verify the results of a positive scratch test. With either test, a positive reaction usually consists of a raised reddish welt, or wheat . The welt should develop within 15 or 20 minutes if that particular allergen is the cause of the symptoms.

Culture Plates

If the allergen has been identified, or if the allergist still suspects a substance in the environment of the patient despite negative or inconclusive tests, the patient may be given a set of culture plates to place around his home and office or work area. If the allergen has been identified, the culture plates can help the physician and patient learn where his exposure to the substance takes place. If the allergen is not known, the cultures may pick up samples of less common allergens that the specialist can test.

Mucosal Test

Another kind of approach sometimes is used by allergists when skin tests fail to show positive results despite good evidence that a particular allergen is the cause of symptoms. It is called the mucosal test . The allergist using the mucosal test applies a diluted solution of the suspected allergen directly to the mucous membranes of the patient, usually on the inner surface of a nostril or by aerosol spray into the bronchial passages. In some cases, the allergic reaction occurs immediately and medication is administered quickly to counter the effects. Because of the possibility of a severe reaction in a hypersensitive patient, the mucosal test is not employed if other techniques seem to be effective.