Allergy testing: most common types of tests
Allergies are an increasingly common health concern for children. According to the American Academy of Allergy, Asthma and Immunology, the rate of allergies in the industrialized world has been rising steadily for 50 years. Today, as much as 40 percent of the population has some kind of allergy, including to foods, plants, insects, drugs, or other proteins. Allergies are more common in children with parents who also have allergies.
If your child is recommended for allergy testing, there are a few methods allergists use to identify specific allergies. The most common tests are skin prick tests and RAST tests.
Skin prick tests are performed by taking common allergens and diluting them. Then a small amount is inserted into the skin with a small prick or scratch with a needle. If the child is allergic to the substance, a reaction is usually seen within 15 minutes in the form of redness and a raised, itchy bump, also called a wheal.
In the case of food allergies, a positive skin test does not necessarily mean the child is allergic to the food but may indicate that further testing is needed. If your child has never had an obvious allergic reaction when eating that food, your doctor will likely perform a blood test to be sure there is a food allergy.
The most common blood test is a radioallergosorbent test, or RAST. This test uses radioactive markers to detect the levels of antibodies in the blood produced in response to the allergen. A RAST test is often performed in very young children to decrease the number of needlesticks needed for testing. In this test, blood is taken from your child’s vein.
Some doctors will perform a skin prick test and a RAST test to get a more clear picture of a child’s allergies if, for example, your child is having skin reactions, but it is not clear which foods are causing them. If allergies are found, your doctor will determine the best way to treat your child. This may involve allergy shots to help your child develop immunity to the allergens, antihistamines to reduce the reaction to the allergens, or elimination of certain foods from your child’s diet.
Takeaways
- Allergies are becoming more common worldwide.
- The most common allergy tests are the skin prick and the RAST test.
- Some doctors will perform both a skin prick and a RAST test, but both tests are 90 percent accurate.
- Once allergies are diagnosed, your doctor may recommend allergy shots, medications, or elimination of the offending allergen.
I didn’t know that a skin allergy test for food isn’t always accurate. When I get the chance, I should see if I can get my blood work tested. It would be good to know what I am and am not allergic to.
http://www.southernallergy.net/services.html
Hi Sarah. Allergy testing is far from perfect and that’s why working with a board certified allergist is really important. They can help you determine if 1. you need testing and 2. how to interpret those tests. If you are not experiencing any symptoms many allergists would advise against routine testing. Testing a broad range of foods when you do not have symptoms can lead you with a lab “diagnosis” of an allergy without a clinical diagnosis – this leads to more questions than answers.
Very good description of skin testing by Dr. Connolly. We now place 10 tests at a time which makes the entire process much quicker and less painful for kids. What Dr. Connolly said about food testing is exactly right….a positive test always needs confirmation by history. In other words, if you can tolerate the food without rash, cough, wheezing, etc, you don’t have a food allergy. As always, medicine is more complicated than a simple answer to food allergy, and you may be experiencing a food intolerance, but that’s a different topic altogether. http://www.TulsaAllergyNews.com
Thank you for your comments, Dr. Wiens! Food allergies are both interesting and complex and we thank you for your thoughtful remarks!
Thanks for the comments, Dr. Connolly. You touched on the “false positive” skin test to foods and it’s very common for patients to have to adverse effects from ~50% of foods that have a positive skin tests. (asymptomatic hypersensitivity). The look of surprise, however, is almost always present when patients have negative tests for allergy. It helps to explain that negative allergy means no IgE and of course, no allergy shots. Parents are often relieved to know that no “everybody” has allergy.
http://www.TulsaAllergyNews.com (Lynn Wiens, MD)