Allergy tests are a way to get to the bottom of what's causing your asthma symptoms. They help your doctor find your asthma triggers and prevent breathing problems.
But allergy tests alone are not enough to make an asthma diagnosis. Your doctor will look at your history of allergic reactions, too.
Several types of allergy tests help with asthma, including skin tests and blood tests. The results of your allergy tests may show what's triggering your asthma and allergy symptoms, and that can help with your treatment.
Allergy Skin Tests
Your doctor may recommend skin tests if he or she thinks a specific allergen is causing your asthma symptoms. Allergy skin tests are quick, fairly reliable, and cost-effective. Your doctor will have test results usually within an hour of the skin test.
If you have poorly controlled asthma, trouble breathing, or a high risk of anaphylactic reactions, your doctor may wait to do skin tests.
Ask your doctor if you need to do anything before the test. For example, you should stop taking antihistamines before you get an allergy test. Your doctor may have other specific instructions, too.
In a skin test, you get a dose of a possible allergen. The test tracks your immune system's response -- specifically, if your body makes a molecule called immunoglobulin E (IgE). A high level of IgE can mean you have an allergy.
Skin Prick Test: The skin prick test is the most common allergy skin test. First, you get a series of tiny drops of allergens on your skin, usually on your back. Then you get a quick needle prick in the skin where each of the drops are. If you're allergic, you'll get a dime-sized hive that's red and itchy at the needle prick site. You may need a follow-up test to check the results.
Intradermal Test: If your skin prick test was negative, your doctor may try an intradermal test. In this test, your doctor injects the allergen into your skin. Intradermal allergy tests are often used for environmental allergies and drug allergies. Doctors usually don't use this type of allergy test with food or latex allergies.
Intradermal tests can be more accurate, but sometimes they may be falsely positive. That means they show that you have an allergy when you actually don't. Intradermal tests are also more likely to cause an allergic reaction that affects your whole body.
Patch Test: Your doctor applies the allergen to a patch. You'll leave the patch on your skin on for 48 hours. If your skin turns red, gets irritated, and itches, the chances are great that you have an allergy.
Allergy Blood Tests
Your doctor may also recommend getting an allergy blood test.
Radioallergosorbent Test (RAST): This test may be less accurate than skin tests, but it's good for ultra-sensitive people who can't get a skin test because they might have a severe allergic reaction. It's also not affected by medications you may be taking. RAST is more expensive than skin tests. Doctors use this test for young children to rule out an allergy to something they breathe in.
Quantitative Immunoglobulin Determination Test: This measures levels of different immune system chemicals in your blood. It can help your doctor determine if your symptoms are caused by an allergy. This test isn't used often.