What is allergy testing?
If you have a stuffy nose, trouble breathing (especially in the summer), or hives after eating certain foods, you may have an allergy. Allergy tests can help you and your doctor find out if these problems are caused by an allergy and which things you are allergic to. That way you can stay away from the things that trigger your allergic reaction.
What kinds of allergy tests are available?
There are several types of specific allergy tests. There are skin and blood tests for allergies.
Immediate-type hypersensitivity (IgE) skin tests are typically used to test for airborne allergens, foods, insect stings, and penicillin. Immediate-type hypersensitivity also can be evaluated through serum IgE antibody testing called radioallergosorbent testing (RAST).
Delayed-type hypersensitivity skin tests (patch-type skin tests) are commonly used in patients with suspected contact dermatitis. Some common allergens for patch testing are rubber, medications, fragrances, vehicles or preservatives, hair dyes, metals, and resins.
About 15 minutes after the application of to skin, the test site is examined for a wheal and flare reaction. A positive skin test reaction (typically, a wheal 3 mm greater in diameter than the negative control reaction, accompanied by surrounding erythema) reflects the presence of mast cellbound IgE specific to the tested allergen.
Skin tests are used most of the time. There are three main kinds of skin tests. The first kind is called a "scratch" or a "prick" test. Positive-control skin tests (histamine) and negative-control skin tests (diluent) are essential for correct interpretation of skin test reactions. A tiny drop of testing allergen fluid is placed on your skin. Then, the skin is pricked through the drop. After 15 minutes, the test site is checked for redness and swelling. There's a "prick" sensation when the testing is applied, but it doesn't hurt a lot. Usually, about 240 prick tests are needed for a full exam.
Intra-dermal Tests: In the second kind of skin test, the testing fluid is injected into your skin (like a shot). This test is used to check for allergy to medicines (most often penicillin) and bee-sting allergy.
The third kind of skin test is called a patch test. A small patch of material soaked in testing fluid is taped on your skin. After 2 or 3 days, your doctor will take off the patch and look for redness and swelling in your skin. Patch tests are used to evaluate rashes caused by allergy to things that might rub against your skin.
Some commonly used medicines, like pain killers and antihistamines, can interfere with skin tests. If you take these medicines, you have to stop taking them before skin tests can be done.
Why should I be tested for allergies?
It is not always necessary to have allergy tests. In some cases, it can be easier to skip the tests and go straight to taking allergy medicines. There are a number of safe and effective medicines that work well for most allergies. If these medicines do not work for you, or if you have severe allergy reactions, allergy testing may be helpful.
Allergy tests can help you find out what you are allergic to. Once you know what you are allergic to, you can try to stay away from it.
Having established a correct allergy diagnosis, the physician is better equipped to select appropriate therapeutic interventions for that patient, such as allergen avoidance, medications, and, sometimes, immunotherapy. For example, a patient with a specific pollen allergy may be instructed to increase medication use during the pollen season. Patients with an animal allergy may be instructed to use allergy or asthma medication before exposure. After specific testing, avoidance measures can be targeted to allergens to which the patient is known to be allergic.
Is allergy testing safe?
A retrospective study2 involving 18,311 patients found six mild systemic reactions over a five-year period.
Is allergy testing accurate?
The sensitivity and specificity of percutaneous testing were 94 and 80 percent for upper respiratory symptoms, respectively; 84 and 87 percent for lower respiratory symptoms; A negative result for percutaneous testing indicated that a true allergy was unlikely.
The performance of percutaneous tests in the diagnosis of food allergy: The sensitivity of percutaneous tests was 90 percent, with specificity 65 percent, depending on the food extract used for testing. Negative reactions to suggested food allergens on percutaneous tests make a diagnosis of true food allergy unlikely in most cases.
Assays for Specific IgE Antibodies
In general, RAST and other laboratory methods for IgE testing are highly specific but somewhat less sensitive than percutaneous tests. Results of laboratory testing for food-specific IgE are generally poor, even less helpful than those for percutaneous skin testing.
RAST or other laboratory testing is typically considered when skin testing is inconvenient or difficult to perform. Most primary care physicians do not have immediate access to a clinical skin testing laboratory, so RAST may be easier to obtain. Some patients cannot undergo skin testing because of skin disease that would obscure wheal and flare results (e.g., extensive atopic dermatitis) or because they cannot stop taking medications that suppress the skin test response. In cases of life-threatening allergy (e.g., anaphylaxis), laboratory testing is sometimes used as a proxy result, keeping in mind its limited sensitivity.
The most common allergy-mediated clinical problem where specific testing may be needed is chronic rhinitis. Many physicians make a presumptive diagnosis of allergic rhinitis based on the medical history. Management of these patients may include use of antihistamines, decongestants, or intranasal steroids. This is a reasonable and effective approach in many patients. In some patients, specific allergy testing may be warranted.
Allergic asthma often shares the same allergic triggers as allergic rhinitis.
It is important to consider allergy and asthma as the manifestations of a hypersensitive "UNITED AIRWAYS."
The second National Heart, Lung, and Blood Institute (NHLBI) guideline on allergic rhinitis & asthma management recommends that all allergic rhinitis & asthma patients who require daily or weekly therapy be evaluated for allergens as possible contributing factors.10 They also note that, in selected patients with asthma at any level of severity, specific allergy testing may be indicated as a basis for allergen avoidance or immunotherapy.
Part of this material is derived from: Copyright © 2002 by the American Academy of Family Physicians. Permission is granted to print and photocopy this material for educational uses.
Initial Management of these patients is MEDICAL, & may include use of antihistamines, decongestants, or intranasal steroids. This is a reasonable and effective approach in many patients.
Allergen immunotherapy may be especially beneficial when avoidance and medications no longer control the patient's symptoms.
In patients with significantly discomforting or disabling symptoms that are NOT CONTROLLED with standard measures, surgery may also rarely be prescribed as an option.
WHERE NASAL OBSTRUCTION IS A PREDOMINANT SYMPTOM, SURGERY REMAINS THE METHOD OF CHOICE FOR AIRWAY CORRECTION.
Surgery may involve any or all of the following :
Reduction of the turbinate size to reduce the sensitivity
Ablation of the vidian nerve (the nerve responsible for a hyper-reactive nose)
Re-establishment of blocked pathways for the sinuses to aerate (allow sufficient oxygen to enter).