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Diagnose & Test

Is allergy inherited?
There are three classic kinds of atopy: atopic dermatitis (eczema), hay fever (seasonal allergic rhinitis) and allergic asthma.Most allergy sufferers are atopic. Atopy means that the individual has a genetic tendency to develop allergies. In mostdeveloped countries up to 40% of the population will be atopic. Even only one-half of them will develop allergic symptoms. Atopic individuals are genetically prone to manufacture antibodies of the IgE class. These IgE (immunoglobulin E) antibodies tend to react against allergens present in the environment (pollen, cat dander, moulds, house dust mite).Atopy is therefore easily diagnosed in an individual who has a personal or immediate family history of allergies and on doing skin prick test they react to one or more of the common environmental allergens.These individuals with the genetic predisposition must be exposed to the allergen either in their environment or in their diet. So allergy is partly inherited and partly environmental. If one of your parents has a respiratory allergy, you have a 30 to 50 percent chance of developing one, though not necessarily the same allergy. If both of your parents have respiratory allergies, the risk that you will develop an allergy goes up to 80%.



Do children outgrow allergies?

Sometimes. Food allergies are more likely to be outgrown than inhalant allergies. Food allergy is much more common in children than adults, because up to 80% of infants will outgrow their allergy to milk and eggs by the age of five.


How is allergy diagnosed?
A good medical history is usually the basis for the diagnosis of any allergy. Knowledge of the family history of allergic problems is very helpful. However, it may take some good detective work to figure out exactly what the allergen is.


Skin Prick Tests

To confirm which allergen is responsible, skin prick tests may be recommended using extracts from allergens such as house dust mites, pollens, or moulds commonly found in the local area. A diluted extract of each kind of allergen is pricked into the skin of the forearm or on the back.

With a positive reaction, a small, raised, reddened area with surrounding flush (called a wheal and flare) will appear at the test site. The results are measured after 15 minutes. The size of the wheal can provide the physician with an important diagnostic clue, but a positive reaction does not prove that a particular allergen is the cause of the patient"s symptoms. It proves that IgE antibody to that specific allergen is present in the skin.


Blood Tests
Diagnostic tests can be done using a blood sample from the patient to detect levels of IgE antibody to a particular allergen. One such blood test is called the RAST (radioallergosorbent test), which can be performed when the entire body is covered with eczema or if the patient is on antihistamines, which will interfere with skin prick test results.


How are allergies treated?
The diagnosis should ideally be confirmed, to determine the exact source of the allergy, before commencing treatment. The best way to treat allergies is to avoid exposure to the allergens in the first place. This is impossible in some cases. Many treatments are available to relieve symptoms, ranging from over-the-counter antihistamines to potent anti-inflammatory drugs like steroids. Immunotherapy, also known as desensitization or "allergy shots" is a method of treating allergies that was developed in 1911. In this method, extracts of the offending allergen are injected in the individual in gradually increasing doses. Thus, the patient is allowed to build up immunity, probably, through an increased production of protective (IgG) antibody to combat the allergic (IgE) antibody.
 

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