Diagnosis
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.
Intracutaneous tests
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
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How is the prick 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. |
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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. |
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Make sure the dropper does not touch the skin, a new lancet must be used for each test solution. |
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The result, such as a lump that may itch slightly, becomes visible after 15 to 20 minutes. |
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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.
Blood tests
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).
Provocation tests
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
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.
