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Allergy Tests for Allergic Rhinitis
Allergic rhinitis occurs when you breathe in allergens leading to inflammation and swelling of your nose and nasal passages resulting in build up of mucus. Hence allergic rhinitis and sinusitis are closed linked to each other. If your Sinus Specialist suspects allergy to be responsible for your sinusitis, you may be recommended allergy tests for allergic rhinitis.
Allergic diseases have increased considerably in recent years despite the advances in the methods of diagnosis and treatment of these diseases. In India, one in every four people suffers from an allergic disease.
Allergic rhinitis is generally triggered by allergens such as pollen, dust mites, pet hair, etc. This causes build up of mucus, nasal secretions and congestion. These in turn cause your sinuses to be blocked. If you are sensitive to certain allergens and allergic rhinitis could be causing your sinusitis episodes.
Several studies have shown that rhinitis is the most common allergic disease worldwide and affects 40% of children and 20% of adults. To establish adequate treatment, whether immunotherapy, avoidance or pharmacotherapy, it is essential to make an accurate diagnosis. Although the clinical history is fundamental for diagnosis, the precise identification of the allergens is carried out through auxiliary diagnostic tests.
In recent years, considerable progress has been made in the development of new diagnostic methods for allergic diseases. The effectiveness of these diagnostic methods used is directly related to the professional technical capacity, the quality of the material used and the correct interpretation of the results. Before taking these tests the patient should avoid the use of certain medications such as antihistamines (loratadine, chlorpheniramine, cetirizine, etc), corticosteroids (prednisone, cortisone, methylprednisolone, etc.) and antidepressants to avoid errors in the diagnosis.
In general, these tests are important for determining or ruling out the allergenic triggers of rhinitis. In addition to their diagnostic purpose, allergic tests for rhinitis also allow the establishing of a specific treatment. Once the allergenic factor that triggers the symptomatology of the patient is identified, an adequate environmental control can be indicated to avoid exposure to the allergen and, therefore, to avoid exacerbations of the symptomatology.
Skin tests have an excellent application in the identification of the allergens that trigger the symptomatology. Taking into account that not all rhinitis is allergic in nature, these tests allow doctors to make a differential diagnosis between allergic and non-allergic conditions.
Skin tests can be classified according to the time in which the results are obtained: immediate reaction tests and delayed reaction tests.
Skin Tests of immediate reaction
The main tests in this group are Puncture Type (PT) and Intradermal (ID) Test. These consist in putting a small portion of the allergenic extract in contact with the skin cells in order to show if there is a wheal or papula formation that demonstrates the presence of specific antibodies for the allergen tested.
In the puncture-type skin test, allergen agents are applied to the most superficial layer of the skin, through a puncture with a lancet 1 mm long. They are usually applied on a flat and depilated surface of the body, preferably the forearm or back. The number of allergens to be used varies according to the clinical history. It is important to know the environment to which the patient is exposed to properly choose the allergens to be analyzed.
The results are obtained after 15 or 30 minutes. A positive response manifests as a weal or papule more than 3 mm in diameter. The puncture method is very safe since it has a low risk of side effects and can be used in children.
The intradermal test is more painful and has a higher risk of generating adverse effects. In this test, the allergen is applied in the deepest layer of the skin and the interpretation of the results is similar to the puncture test.
If a very deep application of the allergen is carried out, it does not come into contact with the skin cells and the test can lead to false negative results.
There is a complementary alternative method, called ‘prick-by-prick’ that uses fresh allergenic extracts to determine if allergenicity exists. It is widely used in cases of suspected food allergy, has a high diagnostic efficacy, but is also more related to serious adverse effects, such as anaphylactic shock in hypersensitized patients.
Delayed Reactions tests
These tests are performed over a longer period of time because the allergic response is of the cell type (T lymphocytes) and the results are obtained after 72 hours of contact of the allergen with the skin cells. The test should be applied to an area of the skin without injury and without hair.
Tests with Specific Allergens
In very few cases, skin tests can produce false positive results; in such cases the diagnosis can be confirmed by serum tests and provocation tests with specific allergens.
Nasal Provocation Test
The nasal challenge test allows a controlled reproduction of the response of the nasal mucosa to the exposure of the allergen. This test allows doctors to identify precisely which agent is involved in the development of the signs and symptoms of allergic rhinitis.
Taking into account that the above are methods of higher risk since the nasal mucosa is exposed directly to the allergen, these tests must be carried out in specialized centers.
Total Quantification of Serum IgE
Immunoglobulin E (IgE) is the main antibody involved in allergic reactions. The quantification of the total IgE is carried out by means of a blood analysis in which different methods are used to determine the IgE values. The possibility of determining the values of total IgE and specific IgE associated with the detection tests of the main environmental allergens allows to establish a more precise diagnosis.
Quantification of Specific Immunoglobulin E
The technique of determination of specific IgE was developed by Wide in 1967, and continues to be used as a complement in the diagnosis of allergic diseases. The specificity and sensitivity vary according to the allergen evaluated.
A negative test does not rule out sensitization to an allergen, and to make the final diagnosis the clinical history and associated specific skin tests should be considered. There are several methods for determining specific IgE in serum, such as ELISA (enzyme-linked immunosorbent assay), FAST (fluorescent-allergosorbent test), MAST (multiple chemiluminescent-allergosorbent test), RAST (radioallergosorbent test). All of them use the principle of ‘allergosorbent’ i.e. allergen linked to a solid support. If the patient’s serum contains specific IgE against the allergen, it binds to it. What varies in these systems is the form of reaction that allows to reveal the result, for example ELISA – a colorimetric enzymatic method and RAST – a radioactive method.
Although more specific, these diagnostic methods are less sensitive when compared with skin tests, and are indicated precisely in patients with a history of anaphylactic reaction in which the skin test is contraindicated.
Other Diagnostic Procedures
Other laboratory tests may be used as alternative methods for the diagnosis of allergic rhinitis, but they are less specific and difficult to perform. For example, in some countries, the quantification of nitric oxide in the exhaled gas is used in the evaluation of patients with asthma and allergic rhinitis.
Diagnostic tests for allergic rhinitis are important to confirm the diagnosis according to clinical evidence, but each case should be studied individually. Although it is not always possible to determine the immunological mechanisms involved in the clinical manifestation of the patient, with diagnostic tests, it is possible to determine (or rule out) at least one mechanism of ‘cause and effect’ which has a greater clinical application. Since once identified, measures can be established to avoid contact with the specific allergen that triggers the symptomatology.