history is the primary diagnostic tool. Laboratory studies, including skin and in vitro tests for specific antibodies, have relevance only when correlated with the patient's medical history. Thus, although confirmation of a diagnosis of allergy generally requires an immunologic (laboratory) test to help identify a specific allergenic agent, an immunologic response is not sufficient to diagnose allergic disease; it means only that a prior sensitizing exposure has occurred. Treatment should always be directed toward current symptomatology, not merely toward the results of specific immunologic laboratory tests.
Allergists use a variety of methods to obtain a history. These include open-ended, nondirected question-and-answer sessions, a series of questions ordered according to a formal protocol to ensure completeness, a structured questionnaire history completed by the physician, and a structured questionnaire history completed by the patient. Many allergists use a combination of these methods.
Despite universal agreement about the primary importance of a patient's allergy history, medical textbooks devote little or no space to this topic, and research on the subject seems to be nonexistent.
The most common in vivo allergy test is the skin test. It is used both diagnostically for individual patients and by epidemiologists to develop estimates of disease incidence and prevalence in a population. Skin testing should be conducted with appropriate positive and negative controls. And for safety reasons, appropriately trained personnel and adequate equipment need to be available to treat any adverse systemic reactions resulting from the test.
One of the major problems with performing allergen skin tests is the lack of well-characterized, standardized reagents. Certain indoor allergenic extracts (e.g., dust mite and cat) now contain standardized amounts of major allergens, but others, such as fungi, are crude preparations of arbitrarily chosen fungi.
There are several in vitro allergy tests used for diagnosis and in clinical research. The radioallergosorbent test (RAST) and the enzyme-linked immunosorbent assay (ELISA) can be used to evaluate levels of IgE or IgG directed against an allergen. Precipitin assays such as the double-immuno-diffusion