There are many ways to diagnose an allergy
If you suspect that you have an allergy, you can visit your doctor, who will review your case history, which means that he or she will ask about your complaints. Your doctor will try to determine what is wrong and discuss your complaints with you.
How is your overall condition?
What exactly is the problem?
When are your complaints the most severe and how long have they been bothering you?
In addition, your doctor will check to see whether you have had allergic symptoms in the past. If there are signs that suggest that you have an allergy, you will undergo a physical examination. A physical examination of the causes of an allergy focuses particularly on the facial skin and scalp (eczema), the eyes (redness) and the nose (blocked, runny, irritated mucous membrane). In addition, your doctor will listen to your breathing and examine the oral cavity and pharynx. There are all kinds of tests available to examine the causes of allergic reactions.
The doctor injects a minute amount of the substance that is suspected to trigger the allergic reaction, the allergen, into your skin. If the skin reddens and/or swells, you are sensitised to that substance.
Prick Tests, how is this test performed?
Make sure the skin is healthy, clean and dry. Special preparations are not required, except that the skin should be allowed to 'acclimatise' for a while in the event of extreme outdoor temperatures. The allergen extracts are placed on the skin, for instance, on the inside of the forearm. The various drops should be spaced at least 4 cm apart to prevent the various extracts from mixing. Make sure the dropper does not touch the skin, a new lancet must be used for each test solution. The result, such as a lump that may itch slightly, becomes visible after 15 to 20 minutes. The treatment for the allergy will be determined on the basis of the patient's complaints and outcome of the tests.
Positive and negative test
Besides the prick test, a positive and negative test are also performed. For the positive test, a drop of histamine is applied underneath the series of allergen extract drops, to which the patient must react. A negative test result may be an indication that the patient has used allergy-suppressing medication, such as antihistamines. This means that the skin test is unreliable and must be repeated at a later time.
The negative test merely contains a buffer solution and the patient should not react to it. If the patient does react, it is a sign of hypersensitivity to any of the ingredients of the buffer solution or he or she is reacting to the prick itself. In that case, a laboratory test (RAST) will be required to diagnose the allergy.
According to the guideline of European allergologists (EAACI), a prick test is regarded as positive if the weal has a diameter of at least 3 mm.
For documentation purposes, the following details need to be recorded:
- Patient's name
- Test date
- Tester's name
- Allergens tested
- Prick test results
How can the use of symptom suppressants influence the results of a prick test?
The use of symptom suppressants may influence the results of the prick test. This becomes visible as the positive test does not react or reacts only slightly. The test is then useless and will have to be repeated. The use of symptom suppressants does not influence the results of a laboratory test (RAST). The use of symptom suppressants must therefore be discontinued for a certain period prior to the prick test.
It is recommended to discontinue their use as follows:
- Modern oral antihistamines: 2-7 days in advance
- Oral corticosteroids: 1 week in advance, in consultation with the doctor
- Tricyclic antidepressants 7 days in advance
- Local corticosteroids do not influence the test and their use does not have to be discontinued, as long as they are not administered to the forearm.
In addition to skin tests, blood tests also reveal the origin of the allergic reaction. For example, the 'RAST'(radio-allergo-sorbent test) method is used to measure the amount of IgE-antibodies against one allergen (grass pollen, for instance).
During a provocation test, the allergen is brought into contact with the eye, nose or lungs. Any allergy to the allergen will reveal itself in the form of a reaction. Food allergy tests involve the administration of capsules containing different concentrations of allergen to determine whether a reaction occurs. Provocation tests are usually performed if the results of other tests are inconclusive.
Lung function test
Allergic symptoms may include constriction of the airways. If you visit your doctor with complaints about the airways, you may have to undergo a lung function test. It tests how the lungs work. How elastic are they? How sensitive are they? What is their volume? The test is also used to see how the lungs react to the administration of histamines, the substance released during an allergic reaction. This is called an aspecific provocation test.
Patch test (Epicutaneous test)
Patch tests are often used when a contact allergy is suspected. Small patches are applied to your back, each containing a different allergen. The result can be 'read' after about two days. If an eczema rash shows, you are sensitised to the allergen in question.
Exposure measurements are carried out to gain an understanding of the level of exposure to allergens. This may involve the collection of dust samples that are examined for quantities of allergen. Such an examination may be directed at all sorts of allergens: from house dust mites in mattresses and carpets to occupational allergens. In addition, air measurements can be performed to determine tree and grass pollen levels. These measurements are also used to broadcast pollen reports on the radio.