Lahey allergists primarily use skin tests to determine whether a patient has antibodies in the skin that react to a specific allergen. These tests use diluted extracts from allergens such as dust mites, pollens or molds commonly found in the local area. The extract of each allergen is applied to a tiny prick or puncture made on the patient's arm or back, or administered intradermally, somewhat like a TB test. With a positive reaction, a small, raised, reddened area (called a wheal) with a surrounding flush (called a flare) will appear at the test site. The size of the wheal gives your Lahey physician an important diagnostic clue, but a positive reaction does not necessarily prove that a particular allergen is the cause of a patient's symptoms.
Skin testing is the most sensitive way to identify allergies in people. However, some patients, such as those with widespread skin conditions such as eczema, cannot be tested using that method. The alternative is a diagnostic test that uses a blood sample from the patient to detect levels of immunoglobulin E antibody to a particular allergen. These tests are known as radioallergosorbent (RAST) tests. A newer blood test methodology, commercially known as ImmunoCAP, is especially effective at diagnosing food allergies in children.