Allergies occur when an individual is exposed to a normally innocuous substance that the body mistakenly interprets as harmful. A defensive response results: the affected cells release chemicals called histamines, which increase the permeability of blood vessels, allowing fluid to carry white blood cells to the affected area. This causes the swelling, redness and irritation commonly associated with skin allergies. Allergy tests can help identify the offending substance.
Percutaneous Tests
The American Association of Allergy, Asthma and Immunology describes skin tests used to detect allergies as being common and "relatively painless." Percutaneous skin tests are conducted by introducing a small amount of the suspected allergen into the skin via a pinprick. If the substance is indeed the culprit behind the allergy, swelling will occur in the tested area.
The Mayo Clinic advises that medications can often interfere with the results of allergy testing by suppressing the allergic response. Doctors may advise patients to cease taking certain medications prior to allergy testing.
Intradermal Tests
Intradermal tests are similar to skin prick tests in that they involve introducing the allergen into the skin to stimulate an allergic response. The Mayo Clinic explains that intradermal tests differ from percutaneous tests due to the process of injecting the allergen deeper into the skin, rather than introducing it through a pinprick.
Epicutaneous Tests
Epicutaneous tests are also known as patch tests. These do not involve injection or puncture of the skin, but rather, the application of an allergen contaminated patch.
Percutaneous, intradermal and epicutaneous tests sometimes administer as many as 40 different allergens simultaneously. The physician systematically applies the allergens in a grid pattern that is recorded so as to keep track of which substance has been applied to each individual area.
The results of intradermal and percutaneous tests occur very quickly after administering the suspected allergens. Epicutaneous tests reveal their results more slowly, over several days.
Blood Tests
In instances where allergic reactions are severe enough to render skin tests unsafe, blood tests may be substituted. A sample of blood is drawn and sent for laboratory analysis. In the lab the blood is analyzed for the presence of antibodies that are specific to the suspected allergens. The results take longer to discern than most skin tests.
Challenge or Provocation Tests
This type of testing is considered the most risky and should only been undertaken with medical supervision by an allergy specialist.
Challenge tests involve inhaling or ingesting a small amount of the suspected allergen. Severe allergic reactions can result from challenge testing, thus the precaution that it should only occur under controlled conditions, according to Medline Plus, a publication of the National Institutes of Health.
