sites. False-negative skin test results are usually due to poor quality, low potency, or lack of stability of the extracts used for testing. Most commercially available extracts exhibit wide variability in the concentration of allergens. Unrefrigerated extracts lose potency rapidly. Stabilizing agents such as glycerine or human serum albumin can improve this situation.

Correlation with Other Tests

Skin tests have been correlated with other tests for diagnosing allergic disease. A reasonably good correlation seems to exist between a strongly positive skin prick test and specific IgE assay by radioallergosorbent test (RAST) (see the discussion in the section below, ''In Vitro Diagnostic Tests"). Similarly, a negative skin prick test and negative RAST also correlate well (H. S. Nelson, 1983). Small reactions to skin prick tests are less frequently associated with a positive RAST. Intradermal tests that are positive with high concentrations of allergens are only occasionally associated with a positive RAST (H. S. Nelson, 1983).

Patients may have positive skin prick tests before they develop allergic symptoms, and the tests may be predictive of future symptoms. In patients with negative histories and negative skin prick tests, the diagnosis of allergic disease can usually be excluded if the extract is of high quality.

Conclusions and Recommendations

A major unknown in skin testing is the identity of the more prevalent allergens involved in many indoor exposures. Studies to characterize these allergens are important for the development of reliable diagnostic reagents. Additional research is needed to identify, characterize, and standardize indoor allergenic extracts used for diagnostic testing.

Research Agenda Item: Develop standardized, well-defined indoor-allergen reagents for skin tests that can be used in clinical diagnosis and research studies.

Despite some relatively minor shortcomings, the value of skin testing has been well established over the past century. When correlated with an appropriate clinical history, skin prick tests often are a useful way of screening for the presence of allergic disease. Using appropriate positive and negative controls, intradermal testing can be used to demonstrate low levels of sensitization when allergy is clinically suspected. However, studies are necessary to determine the optimal concentrations and methods for skin testing and to address the relationship between defined skin test reactions and disease.

With respect to the specificity and sensitivity of skin tests within a

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