responsible: German team; for medical correctness: Dr. Illing
What’s an allergy?
An allergy is an overreaction of the immune system to particular substances. The person suffering from the allergy displays symptoms when exposed to these substances (allergens), which are harmless to non-allergic persons. The actual aim of the immune system is to protect the body from pathogens and foreign substances. In the case of an allergy however the immune system overdoes it and produces symptoms which can be highly unpleasant and make the person ill. The main reason for this is that people who are allergic produce a particular type of antibodies called immunglobulin E (IgE). The reaction between the allergen and IgE antibodies causes the release of substances called histamines which in turn cause particular allergic symptoms in the skin, nose, eyes, lungs, etc. Once the organism has been sensitised to an allergic trigger, then this trigger will be recognised by the immune system immediately with each new contact and can in turn cause symptoms. The amount of the trigger substance need only be minimal to induce these repeating reactions. In rare cases there may even be a life-threatening shock reaction (anaphylaxis).
Triggers / Allergens:
- Pollen from trees and grasses
- Foodstuffs, such as fish, nuts, citrus fruits
- House dust mites
- Animal hair from e.g. cats or dogs
- Insect poison
- Nickel, latex
Reasons for development of the condition asthma
|If one parent has asthma||=||25 % risk that the child will also develop the condition|
|Both parents||=||50 % risk|
|Both parents and siblings||=||70 % risk|
According to the latest studies, it is recurrent colds, sinus and respiratory infections which pave the way for asthma. The mucous membrane, sensitised by the frequent pathogens, can no longer recover between infections and then other irritants are added.
Environmental factors also certainly play an important role (contact withallergens, nicotine…).
Associated conditions are:
- atopic eczema
How is asthma diagnosed? The diagnosis of an allergy and that of bronchial asthma is made in several stages:
- Medical history (anamnesis)
- Physical examination
- Pulmonary function test
- Allergy tests on skin or blood
- Provocation tests, e.g. running tests
- Other additional examinations, such as x-ray, measurement of NO in exhaled air
- subsequent evaluation and consultation
Pulmonary function test (bodyplethysmography)
The most complex method is examination in the pulmonary function chamber (bodyplethysmography). Here even minimal changes can bemeasureds well as changes in the small airways. At the same time, airway resistance can be measured. This shows how much resistance the inhaled air must overcome in the bronchi. In the case of narrowing of the bronchi, respiratory resistance increases.
Thomas (aged 7) has drawn himself during his pulmonary function test.
In the case of acute respiratory problems, an x-ray examination of the lung shows whether there is, for instance, emphysema. In the case of chronic respiratory problems, one has to check for congenital deformities or chronicinflammatory changes in the lungs. In certain cases computer tomography or magnetic resonance imaging ( MRT ) may be required. These tests may be necessary to enable other conditions to be ruled out.
Allergy testing on the skin and blood
Skin tests are the most commonly-used method of examination to identify allergens. The test material can be placed in the skin (prick test, intracutaneous test) or on the skin (epicutaneous test = patch test). If there is sensitisation to a certain substance then the skin reacts with swelling (wheal) and reddening or with excema (blisters and nodes). The severity of the skin reaction also gives an indication of the level of sensitisation. A positive reaction to the allergy test does not automatically mean there is an allergic condition. It simply shows that the immune system has had contact with the relevant substance and reacted to it (= sensitisation). The allergy test cannot however show whether this sensitisation really induces symptoms of illness (= allergy). This limitation applies above all to foodstuffs. In cases of doubt, a provocation test must be carried out (in this case the foodstuff is, for instance, ingested under strict medical supervision). The result of an allergy test can therefore never be evaluated on its own and in isolation but must instead always be assessed together with the medical history and the illness symptoms.
The prick test is carried out as follows:
Allergen applied to the skin in liquid droplets
Then a small prick is made in the skin under the solution
After 20 mins the reaction is measured
Last edited by Langer on November 30, 2010 at 8:18 pm