Allergy Testing: An Important Part of Your Diagnosis

Any specific medical information that follows stems from the following article and is not intended to be taken as definitive or wholly sufficient information. Consult your physician or, in this case, an allergist regarding these topics:

James, T. (2002). Allergy testing.  American family physician. 

http://www.aafp.org/afp/2002/0815/p621.html

When living with food allergies, the irritable symptoms that certain foods can produce serve as a prominent indicator for identifying what foods need to be avoided.   That being said, also undergoing allergy testing is important to be fully diagnosed with a food allergy and to initiate effective management of food allergies.  An official food allergy diagnosis is described as consisting of a medical history, physical examination, as well as an allergy test.  Allergy testing is also a way to legitimately distinguish between food allergies and food intolerances.  Food allergies and food intolerances can easily be confused.  In basic terms, a food allergy is a reaction that is triggered by the immune system to a food allergen while food intolerance is related to issues with other body systems, such as digestive problems, which also trigger unpleasant symptoms.  Allergy testing works to identify the body’s immune reaction to specific allergens.
While many of us have gone through a variety of allergy testing, we also may have been fortunate to outgrow allergies or, less-fortunately, developed allergies later in life.  Both of these occurrences are good reasons to seek out allergy testing as adults.  Tests available include IgE skin tests, challenge tests, and blood tests. IgE skin tests (or immediate type hypersensitivity skin tests) are the most common form of allergy testing. This test involves exposing the skin to a small amount of allergen through making a small indentation or ‘pricking’ the surface of the skin.  A reaction should occur within 20 minutes and appears as a small red swollen bump on the skin (also known as the ‘wheal and flare’). If a test is negative, and there is still a suspicion of a food allergen, an intradermal injection can be performed injecting a small amount of the allergen just under the surface of the skin. The physician will again observe for a small red bump to form.  Challenge testing for allergies involves eating a small amount of the suspected allergen.  As I’m sure you would agree, this is a form of testing that should ONLY be performed with your allergist present.  Finally, blood tests involve drawing blood and performing an IgE assay to determine the IgE antibody levels present in the blood that correspond for certain allergens.

If preparing to undergo allergy testing, it can be beneficial to know the benefits and drawbacks of each test compared to one another.  Skin tests can be preferable because they give the fastest result and are relatively less expensive than blood tests.  A drawback to these tests includes the obvious annoying itching that is produced with a positive test.  As well, this test may not be appropriate for those on certain medications such as medications with antihistamine properties that include anticholinergic medications, phenothiazine, and tricyclic antidepressants. Skin testing may also be contraindicated in those with certain skin conditions such as atopic dermatitis. The risk of undergoing a severe reaction with skin testing is extremely low with one retrospective study in the USA finding that, out of 18,331 participants whom underwent skin testing over a period of five years, only 6 developed mild systemic reactions (James T.). In terms of the sensitivity and specificity of skin testing, this has been shown to vary with food versus environmental allergens.  Another study conducted found that, when percutaneous skin testing for an allergen was done as part of a two-part allergy test that included a challenge test, the sensitivity of the test ranged from 76-98% with a specificity of 29-57% depending on the food being tested for(James T.). For those unfamiliar with these terms, Sensitivity represents the accuracy the allergy test correctly identifying someone who is in fact allergic. Specificity represents how often someone who doesn’t have an allergy is correctly identified as not having an allergy.  Intradermal tests were found to have a higher sensitivity, but also have a lower specificity.  When comparing this to blood tests, which allow for a laboratory test called an IgE assay to be performed, the IgE has found to be more specific but less sensitive than skin testing(James T.).  It is still more common for skin tests to be performed and blood tests to be more useful only when there is some contraindication to a skin test.  In terms of a challenge test, this is usually performed for one of two reasons: the finding of another allergy test was inconclusive or suspicious OR there is reason to suspect an individual has outgrown a certain allergy.  In some cases, a ‘double blind’ challenge test may occur where the individual eating the food and the medical professional are aware whether the individual is eating the suspected allergen or a placebo.  This is to avoid the possibility of a reaction being triggered based on the idea of eating risky food.  As previously mentioned, this test should only be done under STRICT medical supervision.

Whether you are interested in having an allergy test performed in the near future or not, it never hurts to educate yourself on the ins-and-outs of the testing you may undergo. And it is be better educated on managing as well as understanding your allergies!

Caitlyn P.