A great many things can cause red welts on the skin. Thousands of conditions can give you a runny nose. To determine whether or not these are allergic reactions requires a professional diagnosis.
Among the most common and effective methods used to test for allergies are skin or prick tests. These procedures inject or insert a small amount of potential allergen – pollen extract, solution containing animal dander proteins and others – under the skin.
In order for the tests to be effective, it may be necessary for you to discontinue any currently used medication temporarily. Prescription antihistamines such as Allegra (fexofenadine) may take more than a week to clear out of the system. Even Benadryl or Claritin may have to be stopped for a day or two. All these and more can interfere with the accuracy of the test.
During the doctor visit a number of different tests are possible.
A percutaneous test punctures or pricks the skin. Small drops of allergen are scratched into the skin near the surface. It’s useful for diagnosing sensitivity to pollen or mold, dust mite waste, or animal dander, and others.
An intracutaneous test involves injecting the allergen into the skin, usually deeper than a scratch test. It’s preferred when looking for allergies to bee or wasp venom and certain antibiotics like penicillin.
An epicutaneous or patch test is useful for detecting skin allergies, such as sensitivity to latex or perfume. Some individuals have reactions to hair dyes or preservatives, a condition called contact dermatitis. The allergen is applied in the form of a patch worn on the skin for a period of time. The physician then looks for characteristic reactions.
Tests are typically carried out on adults on the forearm. For children the upper back is usually used. None of the tests are painful, even the injections. But, mild discomfort is to be expected if, in fact, an allergy is uncovered. The test, after all, attempts to actually induce an allergic reaction. Itching, swelling, redness and other common allergy symptoms are likely if the individual is allergic.
Ask your allergist in advance which test he or she intends to use. Let the doctor know clearly and in detail your medical history. That way he or she can be prepared for anaphylaxis or any other severe (albeit unlikely) reaction that might occur.
Some patients should not have skin tests. They may be particularly sensitive, or have a condition that makes it unsafe to administer the test. In these cases, blood tests provide†an alternative. Blood tests tend to be less accurate and are usually more expensive. Hence, they are generally used only as a next-best option. But they can provide useful results.
A small sample of blood is extracted and tested. It measures the precentage of IgE (immunoglobulin E) present, a major factor in virtually all allergies. The results are accurate in slightly over two-thirds of allergy cases. Measuring the amount of IgE present gives a good prediction for those who may be allergic, but it is only a probable result. It doesn’t actually measure allergy directly as skin tests do.
Blood tests are often recommended as a precaution for those who might have a severe reaction to a skin test. They’re also frequently used for those considering allergy immunotherapy or allergy shots.
Many individuals have only mild allergies, but the condition can be persistent. Getting a professional test can be a sure way to nail down that fact, in order to initiate the correct treatment.