How is an allergy skin test performed in the diagnosis of allergic rhinitis (hay fever)?

Updated: Dec 26, 2018
  • Author: Javed Sheikh, MD; Chief Editor: Michael A Kaliner, MD  more...
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Answer

By introducing an extract of a suspected allergen percutaneously, an immediate (early-phase) wheal-and-flare reaction can be produced. Percutaneous introduction can be accomplished by placing a drop of extract on the skin and scratching or pricking a needle through the epidermis under the drop. Depending on the exact technique used, this testing is referred to as scratch, prick, or puncture testing.

The antigen in the extract binds to IgE on skin mast cells, leading to the early-phase (immediate-type) reaction, which results in the release of mediators such as histamine (see Pathophysiology). This generally occurs within 15-20 minutes. The released histamine causes the wheal-and-flare reaction (A central wheal is produced by infiltrating fluid, and surrounding erythema is produced due to vasodilation, with concomitant itching.). The size of the wheal-and-flare reaction roughly correlates with the degree of sensitivity to the allergen.

The extract can also be introduced intradermally (ie, injected into the dermis with an intradermal [TB] needle). With this technique, the extract is allowed to contact the underlying dermal tissues, including skin mast cells. Intradermal testing is approximately 1000-fold more sensitive than percutaneous testing. This should be performed with care by qualified specialists. The rate of false-positive results may be high.


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