Skin Testing for Allergies

Many types of allergies can be confirmed with the use of skin-testing. Allergy skin-testing provides valuable information about how your body responds to various substances to which you may become allergic, known as “allergens”.

This fact sheet provides general information on what skin-testing for allergies are, what to expect if you undergo skin-testing, and where to have it done.            We hope that this material helps you better understand the basics of skin- testing for diagnosing allergies. Please keep in mind that this information is not meant to take the place of medical advice from your physician.

Mrs. Lambert struggled for several years to figure out exactly what 5-year-old Tommy was allergic to. She kept charts and diaries, tried various medications, and even withheld some of his favorite foods. Still, she couldn’t pinpoint what really was causing his ongoing allergy symptoms. The pediatrician referred them to a local allergist who recommended skin-testing. Tommy was tested for more than 35 different things — and it became clear exactly what he was allergic to, and how best to treat him.

What is skin-testing for allergies?

Skin-testing is a method that physicians use to see whether a patient’s exposure to specific substances provokes an allergic response. So-called immediate-type skin-testing is used to diagnose the kind of allergies that occur very quickly after exposure to an allergen. Allergies that appear several hours or more after exposure usually are not identified with skin-testing

What is an allergy?

An allergy is an adverse reaction from an immune response to something that contacts the body, is inhaled, or ingested. The reactions include sneezing, wheezing, coughing, itching, skin rashes, stomach pain, diarrhea, or even a fall in blood pressure, which can cause dizziness or passing out. With proper management and education, people with allergies can lead healthy, normal lives.

How is skin-testing for allergies done?

Extracts are made from common allergens. These allergens might include various types of grass, trees, and weeds pollen; mold spores; animal dander; cockroach or dust mite debris; and certain foods. The extracts are placed either on the skin or they are injected just beneath the surface of the skin.

Percutaneous (“Prick”) Method. A drop of each allergen extract is placed on the skin, either the lower arm or back. Then, pricking, puncturing, or scratching lightly breaks the topmost layer of skin under the drops. This pricking allows the extract to seep into the skin.

Intradermal Method. The allergen extract is injected under the first few layers of skin using a very thin needle. This method is more likely than the prick method to give a positive response; however, these results are more often “false positives”.

Quick fact . . . False-positive results are reactions to an extract even though the patient does not develop any symptoms when exposed to the allergen.

How many allergens are usually tested at once?

Depending on a particular patient’s history, anywhere from 10 to about 50 different allergens are tested.

Is skin-testing painful?

Prick skin-testing is not an uncomfortable procedure for most patients. Intradermal skin tests cause some discomfort as the allergen is injected. Either type of skin-testing may also cause some itching.

What do the results of the skin test mean?

After the allergen extracts are placed on the skin, your physician looks for signs of an allergic response. A positive response appears in the form of a raised bump or wheal, surrounded by a red area, or flare. The size of the wheal and flare shows roughly how much allergic IgE antibody you have made to that allergen.

Usually, with a prick test, the raised area must be at least three millimeters (about one tenth of an inch) across to indicate a positive reaction. With an intradermal test, an even larger reaction is required.

A positive test only shows that you have made allergic IgE antibodies to the allergen. It does not necessarily mean that you will have allergy symptoms when you are exposed to that allergen, or that the allergen is a cause of your symptoms. This is one reason why your skin test results need to be carefully correlated with your history by an allergy specialist to determine what you are actually allergic to.

How should patients prepare for skin-testing?

To be accurate, allergy skin tests require that all antihistamines be completely out of your system. You should stop taking all antihistamines three to seven days prior to your skin-testing depending on the particular antihistamine you are taking. You should however continue to take any nasal steroid sprays and all asthma medicines since these will not interfere with skin-testing.

Who should get skin-testing to diagnose allergies?

Skin-testing is useful for anyone who wants or needs to identify specific allergy triggers. Anyone, regardless of age, can be skin tested for allergies.

What happens if the skin test is positive for allergies?

By pinpointing the specific allergens that trigger your allergy symptoms, your physician can create a treatment plan to address your specific symptoms. For instance, if you are allergic to substances such as dust mites or animal dander, you can take steps to limit your exposure to them.

Allergy shots can help treat known allergies. In some cases, your physician may advise immunotherapy — allergy shots — to help treat your allergies. The allergy shot uses an extract containing very small amounts of the specific substances that you are allergic to. Over time, getting the injections at regular intervals can lessen your immune system’s response to these allergens.

Are there any possible side effects to skin-testing?

There are extremely rare reports of patients having systemic allergic reactions to skin-testing such as hives or wheezing, so testing should be performed in a facility capable of treating a reaction should it occur.

What kind of physician does skin-testing to diagnose allergies?

Board-certified or board-eligible allergists/ immunologists specialize in testing for and treating allergies of all kinds.

Does health insurance cover skin-testing for allergies?

Health coverage for allergy testing may vary. Check with your insurance carrier for details. Some things you may want to find out might include:

• Do you need a referral from your internist, family physician, or pediatrician to an allergist or immunologist for skin-testing to diagnose allergies?
• What coverage is offered for pre-existing conditions?

The information provided in this fact sheet should not be a substitute for seeking responsible, professional medical care.

Reprinted with permission from “Asthma and Allergy Answers,” the patient education library developed by the Asthma and Allergy Foundation of America.