Allergy Testing – A Beginner’s Guide

Maybe your doctor brought up the idea of allergy testing, or you just want to learn more about what you might face at your upcoming appointment concerning your problems with allergies. Either way, we hope to answer your questions here.

Allergy testing can involve either skin tests or blood tests. Your doctor is trying to figure out what is triggering your allergies. They are looking for your specific allergens, the items that are the triggers to your allergy symptoms. They will start the appointment by asking you questions about your allergies, aiming at figuring out what might be a trigger. This will guide them in what they will test you for.

Skin tests being carried out on forearm for allergies

Allergy testing image via wikimedia

Skin tests

In a skin test, a small amount of the suspected allergen is placed on the skin or just below the skin to see if a reaction occurs. The test can be done by placing a small amount of allergen laden fluid on the skin, then pricking or scratching the allergen into the skin. Many types of allergen extracts are available from foods to pollens, even including one for dust mites. The testing is usually done on the fore arm or upper back.

A small amount of allergen solution can be injected just under the skin. This may be done if a skin prick is negative on an allergen that was highly suspected of being a problem. The injection test is more sensitive than the skin prick test and may catch something that a person didn’t react to with the skin prick test. Either way of testing (skin prick or injection), you are watching for redness and a wheal to form. The area may become itchy and warm.

When only looking for contact dermatitis, an allergen solution can be placed on a patch which is taped to the skin for 24 to 72 hours to look for a reaction. If the dermatitis occurs the allergen has been found.

Once you know what the allergen is, you should be able to help your skin with local or oral diphenhydramine. Most reactions will go away in about 30 minutes.

 

Blood testsAllergy blood testing

With a blood test your doctor is looking for antibodies against the substances suspected of causing problems. The antibodies are a way for the body to react against an allergen. They are formed with the first exposure, then hang around and wait for the allergen to arrive again, at which time they react against it. Blood tests are not considered to be as sensitive as skin tests, but are often used for people in whom it is not possible to get good skin testing performed.

The most common type of blood test used for this testing is the enzyme-linked immunosorbent assay (ELISA). It checks for immunoglobulin E in the blood. IgE levels are often higher in people who have allergies.Their level should rise after exposure to an allergen that is a problem for you. Specific antibodies can be tested in order to determine allergens. You may be able to imagine testing for various pollens, but there is even a test for dust mites.

A radioallergosorbent test (RAST) or an immunoassay capture test (ImmunoCAP) might also be used to test for a reaction to certain types of allergens. The RAST test is used when looking at latex allergy.

 

Food allergies

Food allergies can be a special situation. They may require both skin prick testing and blood tests, or your doctor could choose food intolerance tests. A food challenge might be done, where a person is given gradually larger amounts of the food to eat, while in the doctor’s office so as to be watched carefully. The final test may be abstaining from the food for a certain amount of time to see if your symptoms disappear. This can be safer than a food challenge.

Read more on food allergy testing here.

 

Summary

This is what you have to look forward to, if your doctor decides on allergy testing. Sometimes it is possible to determine what the allergens are, or at least be close enough as to what the allergens are, just by looking at history. You could find out that you won’t need the testing in the end, but it never hurts to know about it.

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