If someone has symptoms of allergy (including but not limited to hives, breathing symptoms, or stomach problems after exposure to an allergen), that person should seek the guidance of a health care professional to accurately diagnose and treat the condition. There are several methods used to diagnose allergies.
First, in order to diagnose allergies, it is very important that the person gives a thorough history and obtains a physical examination. It is vital to determine if symptoms are consistent with an allergic reaction due to the immune system. Depending on the specific symptoms and physical examination findings, different testing may be used.
How does a doctor test for allergies?
One method is skin testing. Drops of specific allergens are applied to the skin and a special testing device causes a small “scratch” or “prick” through the skin. In people with allergies, cells in the skin called mast cells will cause histamine to make a localized swelling in about 15 minutes that an allergy doctor can measure. The benefits of this test are, the ability to find out results rapidly, its high sensitivity (people with allergies will more likely have a positive skin test than blood test), very good ability to rule-out allergy, and the safety of the test. In general, this test is more easily performed and tolerated compared to blood testing, especially in children. One limitation includes the need for people to stop certain medications such as antihistamines for several days prior to the skin test.
Another diagnostic procedure is blood testing. There are different forms of the test including RAST (radioallergosorbent) tests and ImmunoCAP tests. Each of these blood tests has their pros and cons. They may be used in conjunction with skin tests to help determine if someone currently has or has ‘outgrown’ a food allergy. This test is also helpful if skin testing cannot be performed due to a significant skin rash or medications such as antihistamines that have been ingested recently. Because this is a blood test, the results are not available as rapidly (may take 1-2 weeks) and cost more than skin testing.
A third method is an oral challenge. This is typically used when a doctor strongly suspects that the allergy has been outgrown based on the above diagnostic tests. Because there is still a risk of an allergic reaction, albeit low, it is safer to reintroduce foods under the direct supervision of the allergist. The doctor can determine when this method should be used.
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