This is used to evaluate for an underlying trigger/agent in individuals who develop contact dermatitis. Examples of contact dermatitis are the development of a rash after wearing certain metal jewelry or using a certain skin care product. The suspected agents are placed in the form of patches on the back. The patches are removed 48 hours later. The results are read 2 to 5 days after the patches are removed, and sometimes up to 10 days after removal. You should avoid water and moisture in areas where the patches are placed unless there is a special moisture-proof cover placed over the patches.


It’s the peak of allergy season, and allergens are everywhere. This is the time of the year that you see your symptoms worsen. They may even get so bad that you need to see a doctor. Allergy specialists use testing to determine the environmental factors or foods that a patient is allergic to. Typically, allergists use skin testing or blood testing as their diagnostic procedure, but this leaves many patients wondering which type of testing is better. The short answer is, each test has its own advantages and limitations.

How are Blood Tests and Skin Tests Similar?

Both blood and skin tests work to diagnose allergens by detecting antibodies known as Immunoglobulin E (IgE). IgE’s live in a patient’s blood and skin, recognize allergens and trigger an allergic response, allowing the physician to determine what factors are making the patient’s symptoms flare up. Blood tests detect IgE in the blood, while skin tests detect IgE on the skin.

Advantages of Skin Tests
Generally speaking, skin tests are more sensitive than blood tests, meaning they are more likely to detect allergies that a blood test may miss. Skin tests also require less wait time, as results are typically delivered in 15-20 minutes, rather than the one to two week wait time of blood tests. Skin testing also allows physicians to select a wider range of allergens. For example, at McGovern Allergy and Asthma Clinic, physicians have access to over 150 different environmental and food allergens, allowing them to test for uncommon types of allergies. Blood tests are limited by what allergens laboratories test for—which is usually a much smaller amount than skin tests. Lastly, skin testing is much less expensive than a blood test.

Advantages of Blood Tests
While skin testing may seem like the way to go, there are advantages to blood testing that skin testing simply cannot provide. Skin tests require patients to stop taking anti-histamines five to seven days prior to their test. This is because anti-histamine medications make skin less reactive. Blood tests, however, are not affected by medication. Patients with severe allergies who cannot stop taking medication can benefit from continuing their medication while undergoing a blood test. Additionally, patients with sensitive skin (dermatographia) or hives, can produce false positive results on a skin test, reducing the test’s reliability. Furthermore, patients with eczema or those with severe allergic reactions are also better candidates for blood testing. Lastly, blood testing allows for component testing in food allergies, meaning the test can actually determine the exact proteins in food that a patient is allergic too, and can even predict the severity of his or her allergic reaction.

Which is Better?
There really is no one-size-fits-all allergy test. Your best bet to getting the most out of your allergy testing is to consult with an experienced allergist, like those at McGovern Allergy and Asthma Clinic. A knowledgeable and experienced allergist will determine which type of testing is best for each individual patient—taking into consideration his or her previous medical history and the advantages and limitations of each type of test. Sometimes allergists may even use both types of testing, when results from a blood or skin test aren’t definitively clear.

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