Allergy Testing

Reviewed by: HU Medical Review Board | Last reviewed: January 2023

Many people with asthma also have allergies. Allergens are common triggers of asthma symptoms. Examples of allergens include dust mites, pet dander, and mold.1

Allergy testing can identify allergens causing a reaction. Allergy testing cannot confirm that allergen exposure causes asthma symptoms. Doctors must use your medical history to confirm this. Identifying allergic triggers can help you get the best treatment.2

What is allergy testing?

Allergens are substances that cause your immune system to overreact. An allergic reaction happens when your body thinks allergens are harmful. After you are exposed to an allergen, your immune system releases an antibody called immunoglobulin E (IgE). An antibody is a type of protein.1

Too much IgE can cause airway inflammation. This can lead to symptoms of asthma.1

Doctors use allergy testing to diagnose an allergic condition. Family doctors can do blood tests for common allergies. They may refer you to an allergist. Allergists specialize in diagnosing and treating allergies.1

How does allergy testing help diagnose asthma?

Experts recommend allergy testing for many people with persistent (ongoing) asthma. People with intermittent (occasional) asthma may also get allergy testing. This is because allergens are common triggers for people with asthma. This type of asthma is called allergic asthma.3-5

Allergy tests help diagnose allergic asthma. There are 3 steps to diagnosing allergic asthma:6

  • Identifying the potential allergen (using your symptom history)
  • Showing an allergic reaction to the potential allergen (using skin or blood tests)
  • Confirming that allergen exposure causes asthma symptoms (using your symptom history)

Allergy testing can help you know what triggers to avoid. Avoiding triggers can help reduce your symptoms and the number or amount of asthma drugs you have to use. Allergy testing can also determine the best potential treatments. For example, allergy shots and certain biologics may treat allergic asthma.1

Types of allergy tests

Skin prick tests

During a skin prick test, doctors drop a small amount of a possible allergen on your skin. Then, they prick your skin with a needle through the drop. Doctors may also inject the allergen into the outer layer of skin.2

A skin prick test is positive if the area becomes red and swollen within 15 minutes. This means you may be allergic to the allergen. A more severe skin reaction suggests a stronger allergic reaction.2

A positive test does not confirm that you have allergic asthma. Doctors must confirm that allergen exposure leads to asthma symptoms. They will use your medical history to confirm this.2

Many doctors prefer skin prick tests over blood tests. Advantages of skin prick tests include:6

  • Quicker results (within 20 minutes)
  • Lower cost
  • More visible test result (you can see the skin reaction)
  • More potential allergens can be tested

Allergy specialists must administer skin prick tests. This is because of the risks of a severe allergic reaction. Certain medicines and skin conditions can interfere with skin prick testing. Tell your doctor about your full health history and any medicines you are on.6

Blood tests

During a blood test, doctors send a sample of your blood to a lab. In the lab, they test your blood for IgE. This can identify which allergens your body made IgE to fight. Higher IgE levels suggest a stronger allergic reaction.2,7

A positive test does not confirm allergic asthma. Doctors must confirm that allergen exposure leads to symptoms. They will use your medical history to confirm this.7

Blood tests are easier and less risky than skin tests. They do not expose you to potential allergens. But the results are less certain than the results of a skin test. Doctors use blood tests instead of skin tests in people who:7

  • Have a skin condition
  • Take medicines that interfere with skin testing
  • May not tolerate skin testing for other reasons

Challenge tests

During a challenge test, you inhale or consume a small amount of a potential allergen. An allergist should supervise the test because of the risk for a severe reaction.1

A positive challenge test confirms that allergen exposure leads to asthma symptoms. Challenge tests are usually used for food or drug allergies. Food and drugs are not common asthma triggers. But challenge tests may help diagnose aspirin-induced asthma, for example.1

What are the possible side effects of allergy testing?

Possible side effects of skin prick and challenge tests include allergy symptoms. This includes itching, redness, and swelling. In rare cases, serious allergic reactions can happen. This is why these tests should always be done by an allergist.2

Possible side effects of blood testing include mild pain or bleeding. Fainting during blood testing is possible, but rare.2

These are not all the possible side effects of allergy testing. Talk to your doctor about what to expect with allergy testing. Talk to your doctor about anything that concerns you about allergy testing.

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