Allergy Conditions
Asthma – Asthma Diagnosis
Contents
- Introduction
- Allergens
- Careful Observation
- Laboratory Tests
- Screening Tests
- Specific Allergen Identification
- Skin Tests
- Interpretation of Test Results
- Allergens for which Skin Prick or Laboratory Tests are not available
- Bee Venom Allergy
- Conclusions
The corner-stone of the management of the allergic patient focuses on the accurate identification of the environmental agent responsible for his allergic symptoms. In many cases, with the help of a competent doctor, this can be done by a careful and systematic history.
Investigation of the allergic patient by the doctor broadly has 2 components:
- Evaluation of the patient’s environment
- Evaluation of his immunological responses to substances in the environment which are known to cause allergic symptoms. Once the specific trigger of the patient’s symptoms is identified, avoidance strategies can be formulated and in some instances hyposensitisation by specific immunotherapy can be instituted. Avoidance of the allergic trigger is absolutely essential for allergies which may be life threatening. In such cases it is important for the patient to wear a Medic Alert badge, clearly stating the allergy which has been confirmed by skin or blood tests
Allergens
Substances which cause allergies are called ‘allergens’. There are over 300 environmental agents which are known to cause allergies. Allergens which commonly cause allergic symptoms include house-dust mites, cats and dogs, tree pollens, weed pollens, grass pollens, moulds, food substances (e.g. egg, milk), bee venoms and antibiotics (e.g. Penicillin, Sulphonamides). 80% of allergic children living at the coast are allergic to the house-dust mite.
More uncommonly, people are allergic to occupational substances (e.g. paint, wood dust, rubber, cotton, latex), pets (e.g. rats, guinea pigs, birds and mice), other medications (e.g. anti-inflammatory drugs), and even to certain anaesthetic agents. Rarely patients are allergic to exotic fruits, vegetables, parasites and insects (e.g. anti-inflammatory drugs), and even to certain anaesthetic agents. Rarely patients are allergic to fruits, vegetables, parasites and insects (e.g. mosquito, psychoda flies).
Careful Observation
Allergic individuals have a right to know which environmental factors are responsible for their symptoms. These may be identified by shrewd and careful observation in some instances, but in most cases specific allergy tests are needed to identify and confirm the cause of their symptoms.
Certainly, before specific immunotherapy injections are advised, the allergen must be positively identified.
Two broad types of tests are recommended: laboratory test (i.e. Total IgE, Phadiatop, and RAST test) and skin tests.
Laboratory Tests:
- Screening Tests
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The measurement of Total IgE will indicate if a patient is allergic or not.
If it is unclear if you are allergic or not to inhaled substances, your doctor can order a simple screening test for inhalant allergy, called the Phadiatop test, which can be done by your laboratory. If the Phadiatop test result is positive, you are definitely allergic and further RAST tests should then be done to identify the cause of your symptoms, since these are due to inhaled allergens. It is also possible to identify which broad groups of allergens you are allergic to, using RAST Multi-allergen tests, for groups of related allergens (e.g. weeds, grasses, trees, foods, mites or moulds.
- Specific Allergen Identification:
- A pathologist can also identify the cause of an allergy in the laboratory by studying a small sample of the patient’s blood. If he finds high levels of the IgE antibody to a particular substance, using the RAST test, or CAP RAST, it will confirm that you are allergic to that substance. Laboratory tests are accurate, convenient and have a broader range of allergens than the skin tests. It is possible to test for allergy to over 300 environmental substances in the laboratory. Laboratory test are also more suitable for small babies and patients with eczema in whom skin tests are difficult to perform. The costs of laboratory tests can be greatly reduced by using screening panels of appropriate individual RAST tests.
Skin Tests
Return to Top Skin tests can be performed by your doctor in his rooms or at an allergy clinic of a hospital. A drop of the suspected culprit allergen is placed on the forearm (or back), a small prick is made through the drop on the skin whit a sharp object, and after 15 minutes the development of a raised area (wheal) and reddened area (flare) will confirm that the patient is allergic to the particular substance. Skin tests are painless and give a quick result. It is important that you stop your usual anti-histamine treatments at least 48 hours before skin tests are done, since these may block the results. It is dangerous to skin tests are done, since these may block the results. It is dangerous to skin tests for substances to which individuals are extremely sensitive (e.g. Penicillin, peanuts).
Interpretation of Test Results
Return to Top Skill is required to interpret skin tests and the results of laboratory allergy tests, and this should always be done by an expert. In most instances the result of the skin or laboratory test will fit the clinical picture, particularly with inhaled or infected allergens. However, interpretation of the results of food allergy testing is a little more difficult and in some cases the results of laboratory and skin tests will only serve as a guide to identify the causative food trigger confirmation of the allergy will have to be obtained using a food challenge. You can help your doctor a great deal by carefully recording your symptoms in relation to food ingestion. For food allergy the only form of treatment is specific avoidance. Some individuals are extremely sensitive to specific food allergens, e.g. peanuts, strawberries or shellfish. In such individuals, the diagnosis should be confirmed by a laboratory test since in this situation skin testing, or food challenge tests, are positively dangerous.
Allergens for which Skin Prick or Laboratory Tests are not available
Return to Top In some cases, allergic individuals experience symptoms following exposure to substances for which skin tests or laboratory tests are not available such as food additives, e.g. sulphites, or sulphur dioxide. There are as yet no specific tests available in South Africa for the common food additives, but your doctor should be able to make the diagnosis from the history and using challenge tests. It is important to study the labels on foods or drinks to facilitate avoidance.
Bee Venom Allergy
Return to Top Most individuals will have a mild local skin reaction following a bee sting. This does not mean that they are allergic to bees. If however, they develop a spreading skin reaction, dizziness or a tight chest after a bee sting, this suggests true allergy. It is important that this is confirmed by specific laboratory testing and that the patient should receive a course of specific immunotherapy injections.
Conclusion
Return to Top As a result of a dramatic improvement in diagnostic medical technology in recent years, it is possible to identify the cause of your allergy in over 95% of cases, using skin or laboratory tests. Your doctor is able to arrange these for you and will select which are most appropriate. It is most important that the results of any allergy diagnostic tests are carefully interpreted by a doctor, who has had training in and therefore a good understanding of allergy, so that appropriate further management can be instituted.
Copyright: Allergy Society of South Africa.
Written by Dr
Endorsed by ALLSA.
This information sheet is obtainable from:
| ALLSA P.O. Box 88 Observatory, 7935 Cape Town, R.S.A. |
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