| In
Vitro Testing for inhalant allergies deserves special mention because it is a
proven technique that provides a significant advance in allergy testing. The term "In Vitro" refers to test procedures performed "outside the body," as in a laboratory, as opposed to "In Vivo" procedures performed in or on the body directly, as when allergy skin tests are performed. |
The allergic reaction is complex. It parallels the way the body defends itself against virus and other dangerous "foreign" invaders. Just as an antibody recognizes a virus and attaches itself to it so it may be eliminated, a substance in human blood called immunoglobulin E (IgE) also recognizes and attaches itself to allergens - the substances such as dust and pollens, which cause inhalant allergies. (Inhalants are substances which you take into your body by breathing. These include dust, pollens, molds, animal dander and tiny microscopic organisms called mites.)
Just as there are specific antibodies produced for each specific virus, specific IgE is produced for each allergen. That is, there is one type of IgE specifically for ragweed pollen, another for rye grass pollen, etc. If you have enough of a specific form of IgE in your body to cause a reaction when you breathe in one of these substances, you have an allergy.
During the first stage of allergic reaction, IgE attaches to a special cell in the tissue called the mast cell. This combination forms an allergy "bomb" that is triggered only if it contacts the IgE specific allergen. When this "bomb" explodes, it releases many chemicals, including histamine, which causes the watery eyes, runny nose, congested nose, itchy throat, and the other typical symptoms of inhalant allergies. The more the specific IgE you have, the more allergic to the allergen you are, and the stronger your body's reaction is when you breathe it.
The key to finding out what inhalants you are allergic to is to discover what specific types of IgE are present in your blood, and how much of each type is present. That sounds simple, except that we are dealing with microscopic particles which cannot be seen by the eye or identified even with the most powerful microscopes. We have to locate and measure them by very sensitive chemical tests. And that is where these In Vitro tests come in.
In Vitro tests sound very complicated, but actually they are mechanically fairly simple. Here's how they work.
As was mentioned, every allergic patient makes specific IgE to each allergen that they are allergic to. So if a drop of their blood serum or plasma (the liquid part of the blood that has been separated from the heavy blood cells) is combined with a drop of allergen, and specific IgE antibodies in the serum will attach to the allergen. In the In Vitro tests, the allergen to be tested is bound to plastic or paper, to which the serum is added.
The IgE is measured by adding a weak radioactive marker in the test tube (the Radio-allergo-sorbent test or RAST) or a chemical marker that will produce a color change (the enzyme linked immuno sorbent assay or ELISA test). These markers themselves may then be measured.
Using a tiny amount of blood serum, this test can be repeated to measure numerous allergens. This test is only recommended for inhalant allergens, as other problem substances such as foods do not usually involve IgE, and have to be tested in other ways. However, there may be some special circumstances for which your doctor orders these tests for food allergens as well.
Although the results of In Vitro tests are not available immediately, as are skin tests, they offer the convenience of requiring only one sample of blood to obtain the results for several different allergens. This is especially advantageous for children, as their discomfort is minimized.
RAST tests are very precise. As they indicate how allergic you are to each substance, they help guide your doctor to select a safe initial injection dose. If you are highly allergic to an allergen, your starting doses will be weaker than for those allergens to which you are less sensitive. This allows your treatment vials to be "tailor made" only for you. Older methods of testing could not measure the degree of sensitivity to each allergen before treatment is started. Because of this, it would often require more injections and a longer period of time to reach a therapeutic dose than with In Vitro testing. In Vitro testing can also be as cost effective as the older methods of skin testing.
In Vitro testing is extremely simple for the patient. After a thorough physical examination, your doctor will ask you to fill out a "patient history" form concerning the type of timing of your symptoms, to determine the most likely allergens you may be sensitive to, so these may be tested. Your hose and work environment (pets, trees, plants, etc.) may provide important clues as to which allergens should be tested, it is unnecessary to test for allergens to which you are not frequently exposed.
Next, a sample of blood will be drawn from your arm. The blood sample is sent to a trained laboratory technician for testing. The laboratory sends your doctor a report indicating what allergens you are sensitive to, and how allergic you are to them. After explaining the results to you, your doctor will recommend a program to deal with your allergies. This may include changing your environment (such as eliminating offending substances around your home), medications, or taking allergy injections. With proper management, most symptoms of allergy can be very well controlled.