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Tests and Diagnosis for Seasonal Allergies

By Leo Galland ; Updated August 14, 2017

The first step in seasonal allergy diagnosis is clinical assessment by your doctor. The questions your doctor will ask you are:

(1) Do your symptoms show a seasonal pattern?

(2) Is that pattern consistent with exposure to regional pollen or to outdoor mold spores? Do they fluctuate with the local pollen or mold spore count?

Pollen exposure tends to increase on dry, windy days and decreases with rain. Mold spores, however, are much more variable, some increasing before storms, others increasing with warmer temperatures. There are almost 200 species of allergenic molds, which produce about 150 known human allergens. Unlike pollen exposure, which is strictly seasonal, mold exposure may occur in more than one season, depending upon the species of mold.

The next steps for allergy testing are skin and blood tests.

Allergy Skin Tests

There are two types of skin tests. With either type, a dilute solution containing a small amount of a specific allergen is inserted into the outer layer of skin.

With a puncture, scratch or prick test, a drop of the allergenic extract is placed on the skin and a sharp instrument breaks the skin surface to allow a tiny amount to penetrate.

With an intradermal test, a small amount of the extract is injected just under the skin’s surface with a very thin needle.

The reaction is usually checked after 15 minutes. In either case, a “positive” result, signifying an allergic response, requires the development of a “wheal,” which is a red, raised and sometimes itchy lump at the injection site, and a “flare,” an expanded area of redness that surrounds the wheal. The larger the reaction is visually, the more severe the allergic response. These reactions are due to the release of histamine and other substances caused by exposure to the allergen. Allergy medication must be discontinued at least 24 hours before testing or a false-negative result might occur. The results of skin tests must be compared with responses to positive and negative controls because the sensitivity of skin to the injection itself, unrelated to the allergen being injected, varies greatly among people. Some people simply have very sensitive skin.

Allergy Blood Tests

Blood tests look for the presence of IgE antibodies to the specific allergen being tested or to a panel of potential allergens. The two methods used are the RAST (radioallergosorbent test) and ELISA (enzyme-linked immunosorbent assay). With either method, a tiny amount of the patient’s blood serum is mixed with a purified and specially prepared extract of the test allergen(s). Fluorescent or radioactive tracers then determine if there are IgE antibodies present that bind to the specific allergen.

Skin testing and blood testing can identify the presence of Type 1 hypersensitivity to chosen allergens, but they cannot determine if a person’s symptoms are the result of the allergic reaction, which is clinically determined based upon the response to treatment.

Provocation testing is the only method of testing that can determine if the symptoms a person experiences are the result of exposure to the particular allergen being tested. Sometimes an allergy skin test will provoke symptoms like wheezing in a person with asthma. This is one form of provocation. With bronchial or nasal provocation tests, a solution of the allergen is inhaled into the nose or lungs so that the response can be measured. Because of the danger of serious adverse reactions, provocation tests are only done under carefully controlled conditions, such as a research experiment.

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