Allergy Testing

What to Expect

During the test, your child will be asked to lie flat on an exam table on his or her stomach with his or her back exposed. A member of the clinical team will use alcohol to clean the skin on your child’s back before making a series of marks with a pen or marker. These marks serve as a map for the area of skin being tested for each specific allergen. The number of tests your child's allergist performs depends on your child’s medical history.

Next, a member of the allergy team will use a small device called a probe to apply a small sample of each allergen being tested. The probe quickly pricks the skin, and while it does not cause bleeding, it may cause some mild discomfort. Once all allergens have been applied, your child will need to keep lying on his or her stomach for another 15 minutes.

After 15 minutes, the allergy specialist will examine the areas to determine whether any of the allergens caused a reaction and then score the tests. The doctor will share the results with you and your child and discuss whether environmental changes, dietary changes or medicines will be needed to manage his or her symptoms.

The best way to treat an allergy is to avoid the allergen. The doctor may also recommend treatments like immunotherapy or allergy shots if it is not possible to avoid the allergen.

Types of Allergy Tests

There are three types of allergy tests:

• Skin test. The most frequently used type of skin test (and allergy test in general) is the epicutaneous (or skin prick) test. During this test, a trained allergy team member uses a plastic probe to place suspected allergens into the top layer of skin. A second type of skin test is the intradermal skin test in which allergens are injected into the skin with a very small needle. This type of skin test is seldom used since it tends to cause many false positive responses, is expensive, may result in systemic reactions and is uncomfortable for patients. However, in some cases your child's allergist will offer this type of test to help tease out highly suspicious reactivity. Food allergy testing is always done with a skin prick test—intradermal skin tests are not used for food allergy testing since they often show false positive results.
• Blood test. When compared to skin tests, blood tests are not as reliable for diagnosing an allergy. They are not as sensitive, specific or predictive as skin tests. Your child's allergist may use blood tests to follow the course of a food allergy. The blood test can provide a level of circulating IgE antibodies, and that level may be associated with the risk of having a reaction. The values of circulating IgE to food may decrease over time if your child is outgrowing the allergy. Due to high costs and low accuracy for non-food allergy blood tests, blood testing for other non-food allergens is not recommended.
• Allergen challenge. Allergen challenges are the most thorough and accurate type of allergy test. They can be used to test for food, drug, vaccine or local anesthetic allergies. During an allergen challenge, your child will be exposed to the suspected allergen to see if symptoms occur. If your child’s symptoms are due to allergy, the challenge will be positive. It usually does not take a large amount of exposure to make symptoms appear. Allergen challenges carry some risk because the potential reaction might be serious or even life-threatening. Therefore, doctors at Riley at IU Health only perform challenges under controlled conditions in a specialized allergy clinic. Doctors usually do not do challenges if your child has severe reactions to allergens.

Doctors score allergy tests in many ways. The important thing to note is that the score does not measure how severe the allergy is in the patient. Severity of the allergy is based on the type of reaction caused by the allergen. For example, your child might have a low score on the test but experience anaphylaxis in reaction to the allergen. Alternatively, your child may have a high score on the test and experience only a mild skin reaction. Your child's allergist uses test results to determine only if there is or is not sensitivity to the allergen.

In addition, an allergy test may result in a false positive, which means that the test shows sensitivity but your child does not experience any clinical reaction. The test only shows that an IgE antibody is being made. Therefore, allergy tests are an important part of the diagnosis, but they must be considered with many other things like your child’s medical history and history of exposure to allergens to confirm both the diagnosis and the severity of an allergy. 

Who Can Be Tested

Parents are often told that their children are too young for allergy testing, but this depends on the type of allergy being tested.

In children, the first allergies to cause reactions are food allergies. These can show up as atopic dermatitis (skin irritation). This illness may appear after a child turns 3 months old. Doctors may order an allergy test for infants with dry, itchy, flaky skin who are older than 3 months old to help determine if a food allergy is causing the skin irritation. Other food reactions that can be seen at an early age include anaphylactic shock, hives, vomiting and diarrhea.

On the other hand, testing very young children for pollen allergy is not necessary. This is a frequent concern of parents of children with nasal symptoms or allergic asthma. The development of pollen allergy takes time. It evolves over two to three seasons. There may be other airborne allergens that would be more pertinent, such as house dust mites or cat or dog dander. These are more perennial allergens that can lead to symptoms in a young child with only a year of exposure while pollen allergy takes a few years to develop.