Chapter 9 - Epicutaneous and intradermal skin testing

Abstract

Immunoglobulin E (IgE)-mediated reactions account for majority of allergic conditions. Diagnosis of allergic diseases requires documentation of IgE-mediated allergy. Skin testing helps to demonstrate allergen-specific IgE and is an important tool to diagnose IgE-mediated allergy. Of note, positive skin test reaction indicates sensitization and not necessarily clinical reactivity. Thus skin tests should always be guided by patient’s clinical history and/or symptoms and then interpreted accordingly. Skin tests are rapid, easy to perform, and overall very safe. They are usually very sensitive. However, if skin tests are not performed correctly, they can lead to false-positive or false-negative results. The two common methods of skin testing include prick-puncture testing and intradermal testing. Intradermal tests are more sensitive and more reproducible than prick-puncture testing. However, intradermal testing is associated with a higher rate of false-positive reactions. Prick-puncture tests are the most effective, convenient, and cheapest methods for diagnosing respiratory and food allergy. High sensitivity of intradermal testing helps to optimally diagnose venom and drug sensitivity. Several factors affect the results of the skin tests including medications, allergen extracts, and type of the skin test device. Allergen extracts used for skin testing should be of known composition and potency. A high rate of concordance occurs between skin prick-puncture tests and in vitro tests as well as allergen challenges result. Apart from diagnostic purposes, skin tests are also widely used for other purposes such as standardization of allergen extracts, immunotherapy, and pharmacological and epidemiological studies. Clinicians should consider various techniques of skin testing, indications, and factors affecting skin tests prior to performing the tests.