What is the role of skin tests in the workup of allergic rhinitis?

Updated: Jan 02, 2019
  • Author: Quoc A Nguyen, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Skin tests may be performed.

  • Skin testing is generally considered to be the standard of allergy workup. The classic wheal-and-flare responses result from the interaction between the antigen and sensitized mast cells in the skin.

  • In general, the acute phase starts within 2-4 minutes and reaches a maximum in 10-20 minutes. It may be followed by a late phase 4-6 hours later. A number of factors affect the responses; these include the following:

    • Volume and potency of the antigen

    • Reactivity of the skin

    • Age and race of the patient

    • Area of body tested

    • Distance between the injections and time of day of testing

    • Medications (eg, antihistamines and tricyclic antidepressants)

  • Because of these variables, positive and negative controls must be used to ensure the validity of the results.

  • In addition, patients receiving beta-blocker therapy are at risk for severe reactions, and the drugs should be switched to another class of medication before testing is initiated.

  • Currently, 3 types of skin tests are in use.

    • Prick testing is rapid and safe, and scores are graded from 0-4 according to both wheal and flare responses. However, low-grade sensitivities can be missed. Therefore, the test is often used as a screening tool, which is followed by intradermal testing if necessary.

    • Single-dilution intradermal testing involves injecting 0.01-0.05 mL of antigen into the epidermis. The resulting wheal and flare are measured after 10-20 minutes and graded as in prick testing. This test can be used to detect most low-degree atopies if a 1:500 concentration is used. However, as with prick testing, it does not permit accurate quantitation of the sensitivity to the antigen involved.

    • Progressive-dilution intradermal testing (skin endpoint titration) involves a series of 5-fold dilutions, starting with a concentration that is sufficiently dilute to be nonreactive. Progressively stronger concentrations are injected until a wheal forms. The endpoint is confirmed when the wheal with the next stronger dilution is 2 mm larger than the previous wheal. This endpoint indicates the relative sensitivity of the patient to the allergen and designates the starting point for immunotherapy. This method allows both qualitative and quantitative assessment of sensitivity to the antigen in question.


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