Allergy Testing

The Importance of Allergy Testing

More than 50 million people in the United States have allergies, some of them suffering year-round and others experiencing symptoms only when seasonal pollens fill the air. Regardless of the frequency or severity, the first step in any effective allergy treatment plan is to see an allergist, a physician who specializes in treating allergies and asthma, for testing and diagnosis. Many people with allergies never see a physician for testing because of misconceptions about the procedure. But allergy tests, which have been greatly improved over the years, are now more convenient, accurate and relatively painless. Along with a patient's medical history, the results of allergy testing can confirm that symptoms are the result of allergies rather than some other cause and can identify the specific substances that trigger allergic reactions. An allergist can then determine the most appropriate and effective treatment.

How Are Allergy Tests Performed?

Allergy tests are performed using either skin tests or blood tests and should be conducted by an experienced clinician who will select the most effective testing method based on individual patient conditions.

How Do Skin Tests Work?

There are two types of skin tests: percutaneous, also known as prick-puncture or scratch testing; and intracutaneous, or intradermal, testing. During a percutaneous test, a drop of a suspected allergen (in a purified solution) is pricked or scratched on the surface of the skin. The test is performed on a patient's back or forearm with multiple allergens tested at once. If a patient is allergic to one of the allergens, redness and swelling will appear at the site of the scratch. In addition to confirming the presence of an allergy, the amount of redness and swelling also can help determine the severity of the allergy.

If a prick-puncture or scratch test is inconclusive, a physician may perform an intracutaneous test. During an intracutaneous test, small amounts of purified allergen solution are injected into the patient's arm or forearm. Because the allergen is injected below the surface of the skin, it is a more sensitive test and may produce a false positive result. The test also can cause a systemic reaction.

How Long Does It Take to Get Skin Test Results?

One of the advantages of skin tests is that results are known quickly. Positive reactions usually appear within 20 minutes for both types of skin testing, although patients should expect to remain under observation for at least 30 minutes after testing. Delayed reactions can occur several hours after intracutaneous skin testing, sometimes causing swollen, reddened bumps at the spot where the injections were administered. The delayed reaction usually disappears 24 to 48 hours later, but should be reported to the physician.

Is Skin Testing Painful?

Both types of skin tests are relatively painless, as evidenced by the many young children who undergo testing with little complaint. Prick-puncture tests are only mildly uncomfortable because they scrape the skin without drawing blood.

The intracutaneous test also produces only mild discomfort because it uses only very fine needles just below the surface of the skin.

Do Medications Interfere With Test Results?

Some medications do interfere with skin test results or cause potential medical complications. Fortunately, most asthma medications do not. A patient should never abruptly stop taking any prescribed medications without first checking with their physician. In most cases, allergists advise discontinuing the following types of medications two to four days prior to allergy skin testing: over-the-counter (OTC) antihistamines (Benadryl^®, Chlor-Trimeton^®, Dimetapp^®, Tavist-1^®), prescription non-sedating antihistamines (Allegra^®, Claritin^®, Zyrtec^®), monoaminoxidase inhibitors (Nardil^®, Parnate^®) and tricyclic antidepressants (Elavil^®, Sinequan^®, Wellbutrin^®).

Skin tests cannot be performed on patients who are taking beta-blockers (Inderal^®, Tenormin^®). However, as with any medication, patients should not discontinue medication unless directed and supervised by their physician.

When Are Blood Tests Used?

Blood tests, known as radioallergensorbent testing (RAST), often are used to test for allergies when:

A physician advises against the discontinuation of medications that can interfere with test results or cause medical complications;
A patient suffers from severe skin conditions, such as widespread eczema or psoriasis; or
A patient has such a high sensitivity level to suspected allergens that any administration of those allergens might result in potentially serious side effects.

How Does the Blood Test Work?

A sample of blood is drawn and analyzed for the presence of antibodies to specific allergens.

How Long Does It Take to Get Blood Test Results?

Because the blood samples must be sent to a laboratory for analysis, the process often takes several days. If the results are inconclusive, the allergist must perform the test again and wait for new results.

Which Testing Method Is Best?

Allergists consider prick-puncture tests more reliable, precise, convenient and less expensive than blood tests, which do not always provide accurate and comprehensive results.

A new blood test, called the ImmunoCAP, is now available and may be more accurate than the RAST tests, particularly for identifying food allergies.

Allergy tests alone do not confirm or refute the presence of allergies. All test results, regardless of type, require a trained specialist to interpret the results in conjunction with the patient's medical history.

Are There Risks or Side Effects Associated With Allergy Testing?

Any medical procedure involves certain risks, but the risks associated with skin testing are minimal. Most often the side effects produced by skin testing are limited to symptoms very much like a minor allergic reaction. In very rare cases, reactions can be severe, causing anaphylaxis (a life-threatening reaction that affects many organs of the body simultaneously). That is why it is important to have skin tests performed by expert physicians in a medical facility where appropriate emergency equipment and medications are available.

What Allergies Can Be Tested?

Allergy tests can be conducted for most common allergies including plant pollens, molds, dust mites, animal dander, insect stings, foods and drugs.

Who Can Be Tested for Allergies?

Adults and children of any age can be tested for allergies. However, the appropriate testing method should be chosen for very young or very old patients based on the patient's medical history and personal preferences.