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DIAGNOSIS

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Allergy   DIAGNOSIS

Allergy diagnosis is essential for the appropriate management of allergies. Allergy tests will allow you to know precisely what you are allergic to. Unless you know what you are allergic to, you will not know what foods and environmental allergies are to be avoided. Certain substances like dust, pollen, fungus, pet fur, etc. cannot be avoided. Specific Immunotherapy (guided by allergy tests) will allow you to actually develop “tolerance” or “immunity” to these substances. Immunotherapy is administered in the form of drops containing natural protein extracts of whatever you are allergic to.

Allergy
Diagnosis

  • What is Allergy Testing?
  • What kinds of allergy tests are available?
  • Why should I be tested for allergies?

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 find out what you are allergic to. Once you know what you are allergic to, you can try to stay away from the substances that trigger your allergies ,or if avoidance is not possible, your doctor may prescribe immunotherapy, which is the ONLY known way of changing the natural course of allergy.

Having established a correct allergy diagnosis, the physician is better equipped to select appropriate treatment 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 immunotherapy . After specific testing, avoidance measures can be targeted to allergens to which the patient is known to be allergic.

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 PRICK TESTS are typically used to test for airborne allergens like pollen, dust mites or fungus, foods, insect stings, and penicillin. Immediate-type hypersensitivity also can be evaluated through serum IgE antibody testing called IMMUNOCAP testing or 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.

Skin tests are used most of the time. There are three main kinds of skin tests. The first kind is called 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. About 15 minutes after the application of the allergen to the 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 cell -bound IgE specific to the tested allergen.

There's a "prick" sensation when the testing is applied, but it is not painful. The doctor chooses the allergens, and upto 200 prick tests may be needed for a full exam. The skin prick test is still the GOLD STANDARD for allergy testing.

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. Antihistamines interfere with the development of the wheel and flare reaction and should be stopped before immediate-type skin testing. First-generation antihistamines may be stopped two to three days before testing, but the newer, second-generation antihistamines can affect skin testing results for a minimum of 3 days. Medications with antihistamine properties, such as anticholinergic agents, phenothiazine, and tricyclic antidepressants, also should be discontinued before skin testing. Histamine H2-receptor antagonists (Antacids like Zinetac) have a limited inhibitory effect; these medications may be stopped on the day of skin testing. Systemic corticosteroids nasal sprays and inhalers generally do not significantly suppress the wheal and flare reaction of immediate-type skin tests. Oral steroids should be stopped 3 days before skin prick tests.

Why should I be tested for allergies?

Most patients are able to control their symptoms by 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 & recurring allergy reactions, allergy testing may be helpful.

Is allergy testing safe?

A retrospective study2 involving 18,311 patients found six mild systemic reactions over a five - year period. Millions of tests have been done all over the world, with an excellent safety profile.

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. Food allergies may require more detailed blood allergy testing called COMPONENT TESTS.

Blood tests for Specific IgE Antibodies

Although widely used in the past, serum measurement of the total IgE level is unhelpful in the diagnosis of allergy. Of more clinical use are assays for specific IgE antibodies to suspected allergens.

Assays for IgE antibodies specific to common airborne and food allergens are readily available. IgE antibody tests for venom and drugs have less clinical utility and are not routinely used. RAST was the first widely employed method of detecting IgE antibodies in blood that are specific for a given allergen. Quantitative assays that include a reference curve calibrated against standardized IgE are preferred. It is important to select a reliable laboratory to perform RAST testing. In general, RAST, IMMUNOCAP 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)
Some patients 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.
children may not tolerate skin tests so blood tests are performed for them.




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