EDITORIAL BACKGROUND
ALLERGY TESTING
The Importance of Allergy Testing
More than 50 million people in the United States have allergic diseases. Some of them have symptoms year-round and others have trouble 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 evaluation, testing and diagnosis. Many people with allergies never see a physician for testing because of misconceptions about the procedure. But allergy tests are 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 should be performed by an experienced clinician who first obtains a medical history and does a physical examination. If testing is necessary, it can be done using either skin tests or blood tests, chosen on the basis of individual patient circumstances.
How do skin tests work?
There are two types of skin tests, percutaneous (also known as prick, puncture or scratch testing) and intracutaneous (intradermal) testing. During a percutaneous test, the skin is pricked or scratched to introduce a tiny drop of a suspected allergen (in a purified solution) into 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, a small, itchy red spot that looks a lot like a mosquito bite will appear at the site of the test.
If a percutaneous 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 that may produce a false positive result.
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 15-20 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 skin testing, sometimes causing swollen, reddened bumps at the spot where the testing was done. The delayed reaction usually disappears 24 to 48 hours later, but should be reported to the physician. However, when there has been no immediate reaction, delayed reactions do not signify the presence of allergy.
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. Percutaneous tests are only mildly uncomfortable because they barely nick the skin without drawing blood.
The intracutaneous test is slightly more uncomfortable because it uses very fine needles introduced 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, 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 at least two to four days prior to allergy skin testing: over-the-counter (OTC) antihistamines and prescription non-sedating antihistamines (Benadryl, Chlor-Trimeton, Dimetapp, Tavist-1, Allegra, Claritin, Zyrtec), monoaminoxidase inhibitors (Nardil, Parnate) and tricyclic antidepressants (Elavil, Sinequan, Wellbutrin). Some medications should be stopped a week before testing.
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, once 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 sent to a laboratory to be analyzed for the presence of antibodies to specific allergens. Your doctor needs to be careful that testing is performed by a competent laboratory, because laboratories differ in their ability to provide accurate results.
How long does it take to get blood test results?
Because the blood samples must be sent to a laboratory for analysis, the process takes several days.
Which testing method is better?
Allergists consider skin tests more reliable, precise, convenient and less expensive than blood tests. Innovations in testing technology have made the old radioallergosorbent test (RAST) obsolete. The new methods provide accurate and precise measurements of allergy antibody levels in the blood, and seem particularly useful for identifying some types of food allergies. Both methods are available, and whether one is more appropriate than the other depends on the patient’s specific circumstances.
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 and examination.
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 allergens including plant pollens, molds, dust mites, animal dander, insect stings and foods. Testing for drugs and certain other chemicals is less widely available.
Who can be tested for allergies?
Adults and children of any age can be tested for allergies. Sometimes, very young or very old patients have decreased reactivity to skin testing. For that reason, control substances such as histamine are routinely used when skin testing is done.
For More Information
No matter what the cause of allergy misery, the American College of Asthma, Allergy and Immunology (ACAAI) can help consumers bring their allergies under control. For more information about allergies or asthma, call the College at 1-800-842-7777 or visit its Web site at www.acaai.org. The ACAAI is a professional medical organization comprising more than 4,950 allergists-immunologists and related health professionals dedicated to the clinical practice of allergy, asthma and immunology through education and research to promote the highest quality patient care.