If it seems that year-round, indoor allergens trigger your asthma, your health care provider may recommend different types of allergy testing.1 Examples of these kinds of allergens are dust mites, pet dander, and cockroaches.
Allergic asthma is the most common asthma type.2 For people with allergic asthma, contact with an allergen sets off the immune system. Your body begins to produce antibodies called IgE (immunoglobulin E) to fight the allergen. IgE is responsible for allergy symptoms such as wheezing, coughing, swelling, itching, and runny nose.1,3
Testing can confirm that allergies are contributing to your asthma.4 The tests can identify the specific allergen or allergens that cause a reaction for you. The results of allergy testing can help you and your provider to develop the most effective treatment plan. Treatment of allergies may include avoidance, medications, and immunotherapy.
Where are allergy tests done?
Some family doctors and pediatricians do basic types of allergy testing in their offices. They are typically able to do blood (“serum”) tests, because they can draw the blood in their office and send it to a laboratory. An in-office test is available for children and adults that screens for common allergies in about 20 minutes (cat, dog, two different dust mites, cockroach, various pollens, mold, egg white, and cow’s milk).5,6
Your primary care provider may also refer you to an allergist for testing. Allergists are able to do skin prick testing and challenge tests.
What are the types of allergy testing?
Skin or blood (“serum”) allergy tests are used to test for the airborne allergens that are the most common asthma triggers. Challenge tests are mainly used for suspected food or medication allergies.7
Skin tests are used to check your reaction to airborne allergens, such as dust mite, animal dander, cockroach, mold, and pollen.4 This type of test is also used to test for allergies to insect stings and penicillin. It is not as accurate for food allergies.4
This test is done by injecting very small amounts of the allergen into the skin. The injection is very small – just a prick – and relatively painless.7 If the area around the injection site becomes red and swollen within about 15 minutes, you may be allergic to that allergen.4
The allergy skin test is considered safe, with very little risk of a dangerous reaction involving the whole body.4 Skin testing is less expensive than blood allergy tests and the results are available much more quickly. The skin test is just as likely as the blood test to turn up true allergic reactions. Plus, it is pretty convincing to see the way your body reacts to an allergen.1 However, some medications can interfere with the tests, and not all patients are able to stop their medications in preparation for the test.
Blood (“serum”) tests
These tests are officially called “serologic IgE antibody assays.” This means that a sample of your blood is tested to see if your body has made IgE antibodies to fight certain allergens. Blood tests are useful for identifying airborne and food allergens. They are less useful for detecting allergies to stinging insects.
Blood tests are somewhat easier than skin tests, since the blood can be drawn in a primary care office and processed in many laboratories. Blood tests are used for patients with widespread eczema that would make the skin test difficult. Patients do not need to stop taking medications before the blood allergy tests. Because the test is done on a blood sample, there is no risk of a dangerous, whole-body reaction.4
Challenge tests are mainly used for suspected food and medication allergies.7 The person is given a very small amount of an allergen to take by mouth or inhalation. Challenges are conducted in facilities that are equipped to handle emergencies, in case of a serious whole-body reaction. Food is rarely a trigger for asthma symptoms.1 A challenge test may be used to diagnose aspirin-induced asthma.8
What do the results of allergy tests mean?
A reaction on an allergy skin or blood test must be compared with your experience and history.1,9 It is possible to react to something on the skin test that does not trigger symptoms in real life. It is also possible to have no reaction on the skin test to something that has caused allergy symptoms in the past.
There are some clues about how likely a true reaction is. New blood tests are able to quantify the level of IgE antibodies.5 The higher the level of IgE, the more likely you are to have a true reaction. Higher IgE levels also indicate more severe disease or symptoms. Likewise, a more severe reaction on the skin test suggests that a true allergy is more likely.9
If the test results do not match up with your history, you may need to do more sensitive allergy tests.5
How are the results of allergy testing used?
One of the best ways to reduce your symptoms and need for medication is to avoid triggers. It can be costly or difficult to avoid certain allergens.4 Knowing which allergens trigger your asthma can help you to focus on the most important things to avoid.
Allergy shots may be a treatment option if there is a clear link between an allergen and symptoms.1 Allergy shots are most useful for grass, cats, dust mites, and ragweed allergies. They are less helpful for cockroach or mold allergies. Under-the-tongue allergy treatments were approved by the FDA in 2014 for some grass allergies as an alternative to shots.10
If allergy tests show that a year-round, airborne allergen triggers your asthma, you may be able to take a medication called omalizumab (Xolair).11 Omalizumab blocks IgE, which reduces allergic symptoms and asthma attacks.
How should I prepare for an allergy test?
You may need to stop taking certain medications, such as antihistamines, before an allergy skin test. The length of time you need to stop before the test ranges from two to ten days, depending on the type of medication you are taking.4 Your allergist will give you exact instructions. You also may need to stop taking other medications that work like antihistamines. Ask your allergist about the medications you are taking. Most people can continue to take inhaled and oral corticosteroids.4