Dictionary of Allergies .. Atopy diagnosis

The diagnosis of atopy in clinical practice is frequently based on skin tests using a combination of allergens. Usually this involves the application of single dilutions of the allergens  to be tested, introduced epicutaneously by the method of Pepys. A skin weal response greater than or equal to 2-3 mm in diameter is conventionally regarded as a positive reaction.

Skin-prick test thus performed give quick and reasonably reliable results, and are extremely safe. The drawbacks to the technique are the intrinsic variability of the weal response, with a coefficient of variation ranging from 105 to 40% depending on the skin area tested and the size of the weal response, and the need to discontinue antihistamine therapy. In addition the results are unreliable in the presence of dermographism. The measurement of circulating serum levels of specific immunoglobulin E (IgE) can

be used as a an alternative to skin prick testing. The use of the radio-allergosorbent test (RAST) for specific IgE has been shown to correlate with the results of skin prick tests and accords at least as well with patients' clinical history of allergic disease, and the results of direct allergen provocation.

References

Fimerty, J.P., et al: Relationship between skin-prick tests, the multiple allergosorbent and symptoms of allergic disease. Clin. and  Exper. Allergy, 1989:19:51-56.