What is allergy?
Why is it important to test for allergies?
An
allergy
is an unpleasant physical reaction that a person experiences when the body is exposed to a substance to which that person is hypersensitive. Such substances, which are harmless to many people, are called allergens.
Allergy
can affect a wide variety of organs in the body and manifests a range of symptoms.
Nose Nasal itching, congestion, sneezing, postnasal drip, watery discharge commonly associated with "hay fever", or allergic rhinitis
Eyes Itching - redness, swelling, tearing and other conjunctivitis symptoms
Ears Fluid - in middle ear, recurrent infections
Lungs Asthmatic - symptoms such as shortness of breath, wheezing, tightness in the chest, coughing
Skin (including lips, inside of mouth/ears) Itchy welts or "hives" (urticaria) of varying sizes
Skin (contact dermatitis) Blistery rash, intense itching
Skin (eczema) Dry, itchy rash
Digestive Tract Stomach cramps, vomiting, diarrhea (associated with food allergy)
How is allergy diagnosed?
The diagnosis of allergy begins with assessment of the patient's clinical history and symptoms.
Allergy testing
may then be used to identify the specific causes of the allergic reaction.
Traditionally, a patient was tested for allergy by applying a small quantity of allergen to a puncture in the skin and measuring the reaction that develops. Skin testing is qualitative and highly technique-dependent and may result in some discomfort for the patient.
Now, advanced technology is available that permits the physician to diagnose allergy from a blood sample. The test quantitatively measures immunoglobulin E (IgE) that is specific to the allergens being tested. A single blood sample can provide allergen-specific IgE test results to a variety of allergens, allowing primary care physicians the opportunity for early diagnosis and treatment of allergic patients.
Diagnostic allergy testing can play an important role in assessing the potential of atopic disease in symptomatic patients. Accurate diagnosis of allergen sensitivity can allow health care providers to develop an optimal therapeutic approach.
Early diagnosis and treatment of the allergic patient has been shown to modify the course of the disease and prevent subsequent development of other conditions such as asthma. As reported in the Expert Panel Report 2 funded by the National Institutes of Health, atopy, the genetic state of hyperresponsiveness to allergens, is the strongest identifiable predisposing factor for the development of asthma. It has been hypothesized that allergic sensitization at a young age results in a state of chronic airway inflammation, which increases the child's susceptibility to nasal and ear infections. Chronic allergy-mediated inflammation and associated infections can cause mucosal damage and lung remodeling that can ultimately lead to asthma.
A number of studies, including one published in the 1999 World Health Organization ARIA Workshop Report, indicate that early treatment of allergy can change the course of disease progression, with clinical intervention appearing the most effective if treatments are initiated before the age of six. This finding emphasizes the importance of early diagnostic testing.
Allergy Testing
Allergy tests are any of several tests used to determine the substances to which a person is allergic.
There are many methods of
allergy testing
. Among the more common are the skin tests, elimination-type tests, and the radioallergosorbent test (RAST).
Skin tests are the most common. Specific methods vary. The
scratch test
(one of the most common methods) involves placement of a small amount of suspected substances (allergens) on the skin (usually the forearm, upper arm, or the back), and then scratching or pricking the skin so that the allergen is introduced under the skin surface. The skin is observed closely for signs of a reaction, usually and redness of the site -- a controlled hive with so-called wheal and flare. Results are usually obtained within about 20 minutes, and several suspected allergens can be tested at the same time.
Food Allergies
are usually tested by using various elimination diets -- the suspected foods are eliminated from the diet for several weeks and then gradually re-introduced one at a time while the person is observed for signs of an allergic reaction Because a person might believe he or she is allergic to a certain food, a double-blind test may be advised to find out if this is true. In a double-blind test, suspected foods and placebos (harmless substances) are given in a disguised form. The person being tested and the provider are both unaware of whether the substance tested in that session is the placebo or the food substance. A third party knows the identity of the substances and identifies them with some sort of code. This test requires several sessions if more than one substance is under investigation.
While this strategy is useful and practical for mild allergic reactions, it must be undertaken carefully in individuals with suspected severe reactions to foods. In this instance, blood tests may be a safer first approach, as described below. Of note, skin testing is almost never performed to detect
food allergies
for the same reason of the higher risk of causing a severe allergic reaction.
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Allergies - Food Allergy
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