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Allergy Testing

Substance that trigger an allergic reactions are called an allergens. To determine which specific allergens triggering your allergies, your allergist may perform special testing.  Such testing is usually done on your skin, but may, on certain occasions, involve testing your blood for antibodies involved in allergic reactions, such as type specific IgE. Allergy tests are designed to gather the information so your doctor can determine what allergens cause your symptoms and to what degree you are sensitive to these substances. This helps your allergist to determine the best course of treatment for you.

Should you be tested for allergies?
If you are experiencing the following symptoms, the chances are that you should be tested for allergies:

• Any of the following upper respiratory symptoms: itchy or watery eyes, runny nose or persistent nasal congestion, persistent or recurrent soar throat; chest tightness, difficulty breathing or wheezing.
• Skin conditions, including: hives, itchiness or atopic dermatitis (eczema).
• Other symptoms which may indicate the need for allergy testing are: anaphylaxis (a severe life-threatening allergic reactions); abdominal symptoms including cramping or diarrhea, consistently following particular foods; stinging insect reactions, including large local swelling at the sting site.

Generally, inhaled allergens including dust mites, mold spores, and plant pollens will produce respiratory symptoms.  Ingested (food) allergies will generally produce skin and/or gastrointestinal symptoms or anaphylax. But both types of allergens (ingested and inhaled) can produce the gamut of allergy symptoms, including asthma, bronchospasm, rhinitis, urticaria and upper airway disease. 

Why have allergy skin testing?

To help you manage your allergy symptoms, your allergist must determine what is causing your allergy. Allergy tests can identify the specific allergens that provoke your allergy symptoms. Once you have identified these allergen(s), you and your physician can develop a treatment plan aimed at controlling or eliminating your allergy symptoms. For example, if you are allergic to house dust, but not cats, your allergist does not need to recommend that you find other accommodations for the family pet. Some allergens respond better to avoidance whereas your allergist my recommend pharmacologic therapy or allergy shots (immunotherapy) for others.   Decreasing your allergy symptoms can help you return to a more normal life. For example, decreased congestion can improved sleep quality and increase exercise tolerance.  With allergy treatment, you should experience relief from other  allergy symptoms, such as sneezing and blowing your nose, urticaria, atopic dermatitis (eczema), itchy watery eyes and asthma. 

Which allergens will I be tested for?

When your physician makes a diagnosis of allergies, this means that some allergen is causing your —itching, swelling, sneezing, wheezing, or other allergy symptoms.

Allergens are typically made up of proteins. Allergy tests determine which of these proteins (allergens) you react to.  The Allergens listed below are the most common causes of allergies.  Allergists can safely test for allergies to these allergens using allergen extracts that have been standardized by the U.S. Food and Drug Administration (FDA).

The most common allergens (proteins causing allergies) include:

• Parts from dust mites: these are tiny bugs (so small you can’t see them) that live in the dust inside of your house. 
• Proteins from animals (but usually not their actual hair); these include dander (found on their skin), saliva or urine; cats, dogs and horses are among the most common animals that make allergens which cause allergies.
• Mold spores, which are usually found outside, but may also be part of the dust inside of your house.
• Plant pollens from trees, grass and weeds and cockroach parts.

Other serious allergic reactions can be caused by: 1) venoms from the stings insects, such as bees, wasps, yellow jackets, and fire ants. 2) foods, especially peanuts, strawberries and egg whites. 3) natural rubbers or latex found in gloves or balloons. 4) medications such as penicillin.

Who can be tested for allergies?

Adults and children of all age can be tested for allergies. But not all patients must be tested for all allergens.  Your allergist will take a careful history to decide which allergens are the most likely cause of your symptoms to determine which tests and which allergens to use in determining the cause of your allergic disease.

How to prepare for testing:

Some medications can interfere with skin testing. Antihistamines and other medicines can interfere with allergy testing and should be stopped one to several days before your test.  Please carefully review the instructions on allergy testing to be sure you are not taking any of the listed medications or call one of the allergy nurses who will be happy to assist you in preparation.

Types of Allergy Tests

Prick Technique:
Prick testing (or skin testing) is the most common method of testing for allergies. Most Allergists choose to use skin testing because it is safe, reliable and the results are available quickly, giving your allergist the information needed to design a treatment plan that is right for you.

This kind of allergy testing involves placing a small amount of the allergen on the skin, usually on a person’s arm or back.   If you have an allergy, the specific allergens that you are allergic to will cause a chain reaction to begin in your body.  You will see a red area and may itch in the place where the allergen to which you are allergic is placed on your skin.

In people with allergies,  an antibody called IgE (immunoglobin E), causes cells called mast cells to release chemical mediators, such as histamine, that causes redness and swelling. During testing, swelling will occur in the spots where the allergen to which you are allergic are placed. If you are allergic to cats, but not dust mites, the spot where the cat allergen touched your skin will swell, forming a small tiny hive. The spot where the dust mite allergen scratched your skin will remain normal.

The prick tests usually give results (tells you what you are allergic to) in 15-20 minutes. Usually, the only side effects include some itching and redness at the sites where you are allergic.  This usually subsides in less than half an hour. 

This kind of test is usually performed when the prick test gives equivocal results.  In other words, your skin isn’t quite sensitive enough to be sure you are not allergic to a particular allergen.  When this happens, your allergist may choose to have the nurse place a tiny drop of antigen just under the skin, where you will be even more sensitive.  Like the prick test, the intradermal test will show a tiny red bump, that may also itch, when an allergen to which you are allergic is placed.  The test takes about the same time as a prick test and they symptoms go away just as quickly.

Other Allergy Testing Techniques

Scratch tests: 
This kind of testing, in which the skin is abraded before the antigen is placed, is not used very commonly any more.  But may still be used if the allergist feels it will help to reveal the allergens causing your symptoms. 

Challenge testing: 
This test is usually reserved for food or medication allergies.   A small amount of the allergen is introduced into your system (sometimes under your tongue, orally or through inhalation).   Since this kind of testing can cause severe reactions, it must be carefully supervised by your allergist. 

Blood test:
Blood tests are now available for some types of allergies.   These tests are called RAST tests, which stands for radioallergosorbent test.  Because this requires blood to be drawn, this kind of test is more expensive and time consuming than skin testing.  For these reasons, skin testing is usually the preferred method of testing, though your allergist may choose to use some blood testing in conjunction with skin testing to follow changes in your allergies over time.

RAST tests are most often used when skin tests cannot be performed, for example in patients taking certain medications or who have medical conditions that make other kinds of testing impossible, for example, patients who have severe skin conditions like psoriasis or severe eczema in areas that are usually used for testing.

How to prepare for testing:

Some medications can interfere with skin testing. Antihistamines and other medicines can interfere with allergy testing and should be stopped one to several days before your test.  Please carefully review the instructions on allergy testing to be sure you are not taking any of the listed medications or call one of the allergy nurses who will be happy to assist you in preparation.

When to see an allergy and asthma specialist:

Allergy testing by an allergist may help people with anaphylaxis (systemic allergic reaction), asthma, allergic pneumonia, conjunctivitis, cough, dermatitis, drug allergy, food allergy, insect allergy, rhinitis, sinusitis, urticaria and angioedema.

Your allergist can provide you with more information on allergy testing.
Copyright © 2008-2010 Dr. Beth Cowan