Allergy Tests

Allergy testing is important because those that suffer from allergies may be experiencing discomfort and symptoms that could be treated. Also, some allergies are potentially dangerous, and thus, knowing if you are allergic can be a matter of safety.

There are really only two ways to test for allergies, a skin test or a blood test. Basically, this means that if you are going to be tested for allergies, you will either have a skin or blood test to find out what substance, or allergen, may trigger an allergic response in your system. Skin tests are usually the first choice for testing for allergies due to the fact that they are rapid, reliable, and generally less expensive than blood tests, but either type of test may be used.

Let's take a look at the differences between the two tests, and what will happen if you were to get one of these tests:

Skin tests

When you have a skin test done what the administrator of the test will do is put a small amount of a suspected allergen on you. It is placed on or below the skin to see if a reaction develops.

There are three types of skin tests:

Type one: Skin prick test.

How it is done:

In order for this test to be done, a drop of a solution containing a possible allergen is placed on the skin. Then, there is a series of scratches or needle pricks which allows the solution to enter the skin.

Once the above step is done, your skin is observed, if the skin develops a red, raised itchy area (called a wheal), then you are probably allergic to the allergen. When this happens it is referred to as a positive reaction.

Type Two: Intradermal test.

How it is done:

In order for the administration of this test to occur, a small amount of the allergen solution is injected into the skin. Usually this test is done if you get a skin prick test without a positive reaction to a solution, but you are still suspect that the allergen is something you are allergic to. The intradermal test is more sensitive than the skin prick test but is more often positive in people who do not have symptoms to that allergen (false-positive test results). So, you may react even if you are not actually allergic.

Type three: Skin patch test.

How it is done:

This particular test takes longer than the other two, and tests for more specific allergic reactions or symptoms, namely contact dermatitis. For a skin patch test, the allergen solution is placed on a pad that is taped to the skin for 24 to 72 hours to see if a reaction occurs.

Blood tests

Allergy blood tests are usually not as accurate as skin tests, which is why they are usually the second choice if skin tests are not possible, or if they do not get the results one expects. When you have a blood test, basically, what the administrator is doing is they will look for substances in the blood called antibodies. Blood tests are not as sensitive as skin tests, so they are often used for people who are not able to have skin tests. If you have antibodies for a specific allergen, then there is a chance you are allergic to it.

There are a few ways that blood tests are done:

The most common type of blood test used is the enzyme-linked immunosorbent assay (ELISA, EIA). What this test does is it measures the blood level of a type of antibody (called immunoglobulin E, or IgE) that the body may make in response to certain allergens. If you are allergic to something, or if you have asthma, there is a pretty good chance that IgE levels are going to be higher in your system.

The other options for blood tests include lab testing methods, such as radioallergosorbent testing (RAST) or an immunoassay capture test (ImmunoCAP, UniCAP, or Pharmacia CAP), may be used to provide more information. However, like the ELISA test, they all do pretty much the same thing, test for the level of antibodies you have to a specific allergen and determine if you are high for the count.

When to test for allergies

So, what kind of allergies can you test for with these allergy tests? Well, it depends on the test, and there is not one hundred percent accuracy, but it is a good way to rule out allergies, or confirm suspicions.

You can do the skin prick test for the following reasons:

• In order to identify inhaled (airborne) allergens. These allergies are things such as tree, shrub, and weed pollens, molds, dust, feathers, and pet dander.
• In order to identify likely food allergens. Some good examples of these include eggs, milk, peanuts, nuts, fish, soy, wheat, or shellfish. Enzyme-linked immunosorbent assay (ELISA) can find out the foods that a person is most allergic to.
• In order to determine whether a person may be allergic to a medicine or insect venom.

It is good to test for such things before you are at risk because you do not know how severe your reaction may be, and if you are tested and react you can talk with your medical professional about treatment options, how to relieve the symptoms, and what you should do if you have a severe reaction such as anaphylaxis.

Blood tests are used to identify similar allergens, but it is important to note that a blood test or a blood sample may be done instead of a skin prick test if a person:

• Has hives or another skin condition, such as eczema, that makes it hard to see the results of skin testing.
• Cannot stop taking a medicine, such as an antihistamine or tricyclic antidepressant, that may prevent or reduce a reaction to a substance even when a person is allergic to the substance.
• Has had a severe allergic reaction (anaphylaxis).
• Has had positive skin tests to many foods.

How to get ready for allergy testing:

Allergy tests are not entirely accurate and can be affected greatly by medication you may be on. So, to get ready for your skin test for allergies you want to be sure to talk to your medical professional, tell them you want to get allergy tested and ask them to consider all of your medication, prescribed or otherwise, to determine if it will affect your test. If you are serious about having more accurate results you may have to stop taking some medicines, such as some tricyclic antidepressants and antihistamines such as cetirizine (Zyrtec), fexofenadine (Allegra), and loratadine (Claritin) for at least a few days before you have an allergy skin test.

If you are worried about getting ready for your allergy test, simply talk to the health professional that will be administering it, and ask them what you should do to prepare. They will know more specifically to your case what course of action should be followed.

How are they administered?

Skin tests

The health professional doing the skin prick or intradermal test will start by making sure that the skin is clean. They will usually rub it with alcohol, then they will place drops of the possible allergen on your skin a few inches apart. Then, they will prick the skin underneath each drop of allergen with a needle in order to penetrate the skin.(For the intradermal test, a needle is used to inject the allergen solution deeper into the skin.) They will then check the skin after about fifteen minutes and look for red, raised itchy areas called wheals. If a wheal forms, they will conclude that you are allergic.

If the skin prick test is negative, you may choose to have an intradermal skin test at a later visit. A skin prick test is usually done first because the intradermal test has a greater chance of causing a severe allergic reaction.

The test is fairly quick, taking less than an hour.

A skin patch test also uses small doses of the suspected allergen. Only instead of pricking your skin, the patches are placed on the skin (usually on your back). You will wear the patch for one to three days, and you can't shower or participate in activities that make you sweat or the patch will fall off. After the time, the patch will be taken off, and your ski will be checked to see if you have had an allergic reaction.

Blood test

Basically for this test the health professional drawing your blood will draw it just like they do for any other blood test. You will not be exposed to an allergen, instead they collect your blood, give you a band-aide and then they test the blood in the lab.

The blood sample will be placed on specially treated paper and sent to a lab to determine whether antibodies to any of the allergens being tested are present. If specific antibodies are detected, it may mean you are allergic to a certain allergen.

Once you have had your allergy tests done, a medical professional can discuss the next steps you will want to take, depending on the results of the tests.