Allergic Rhinitis Workup

Updated: Apr 10, 2017
  • Author: Javed Sheikh, MD; Chief Editor: Michael A Kaliner, MD  more...
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Workup

Laboratory Studies

Testing for reaction to specific allergens can be helpful to confirm the diagnosis of allergic rhinitis and to determine specific allergic triggers. If specific allergic triggers are known, then appropriate avoidance measures can be recommended. It is essential to know which allergens a patient is sensitive to in order to perform allergen immunotherapy (desensitization treatment). To an extent, allergy testing provides knowledge of the degree of sensitivity to a particular allergen. The most commonly used methods of determining allergy to a particular substance are allergy skin testing (testing for immediate hypersensitivity reactions) and in vitro diagnostic tests, such as the fluorescence enzyme immunoassay (FEIA), for example ImmunoCAP, which indirectly measures the quantity of specific IgE to a particular antigen.

Allergy skin tests (immediate hypersensitivity testing) are an in vivo method of determining immediate (IgE-mediated) hypersensitivity to specific allergens. Sensitivity to virtually all of the allergens that cause allergic rhinitis (see Causes) can be determined with skin testing.

By introducing an extract of a suspected allergen percutaneously, an immediate (early-phase) wheal-and-flare reaction can be produced. Percutaneous introduction can be accomplished by placing a drop of extract on the skin and scratching or pricking a needle through the epidermis under the drop. Depending on the exact technique used, this testing is referred to as scratch, prick, or puncture testing.

The antigen in the extract binds to IgE on skin mast cells, leading to the early-phase (immediate-type) reaction, which results in the release of mediators such as histamine (see Pathophysiology). This generally occurs within 15-20 minutes. The released histamine causes the wheal-and-flare reaction (A central wheal is produced by infiltrating fluid, and surrounding erythema is produced due to vasodilation, with concomitant itching.). The size of the wheal-and-flare reaction roughly correlates with the degree of sensitivity to the allergen.

The extract can also be introduced intradermally (ie, injected into the dermis with an intradermal [TB] needle). With this technique, the extract is allowed to contact the underlying dermal tissues, including skin mast cells. Intradermal testing is approximately 1000-fold more sensitive than percutaneous testing. This should be performed with care by qualified specialists. The rate of false-positive results may be high.

In vitro allergy tests, ie, FEIA, allow measurement of the amount of specific IgE to individual allergens in a sample of blood. The amount of specific IgE produced to a particular allergen approximately correlates with the allergic sensitivity to that substance. These tests allow determination of specific IgE to a number of different allergens from one blood sample, but the sensitivity and specificity are not always as good as accurate skin testing (depending on the laboratory and assay used for the FEIA). As with skin testing, virtually all of the allergens that cause allergic rhinitis (see Causes) can be determined using the in vitro specific IgE, although testing for some allergens is less well established compared to others.

Testing every patient for sensitivity to every allergen known is not practical. Therefore, select a limited number of allergens for testing (this applies to both skin testing and in vitro specific IgE). When selecting allergens, select from among the allergens that are present locally and are known to cause clinically significant allergic disease. A clinician who is specifically trained in allergy testing should select allergens for testing.

Total serum IgE

This is a measurement of the total level of IgE in the blood (regardless of specificity). While patients with allergic rhinitis are more likely to have an elevated total IgE level than the normal population, this test is neither sensitive nor specific for allergic rhinitis. As many as 50% of patients with allergic rhinitis have normal levels of total IgE, while 20% of nonaffected individuals can have elevated total IgE levels. Therefore, this test is generally not used alone to establish the diagnosis of allergic rhinitis, but the results can be helpful in some cases when combined with other factors.

Total blood eosinophil count

As with the total serum IgE, an elevated eosinophil count supports the diagnosis of allergic rhinitis, but it is neither sensitive nor specific for the diagnosis. The results can sometimes be helpful when combined with other factors.

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Imaging Studies

Radiography

While radiographic studies are not needed to establish the diagnosis of allergic rhinitis, they can be helpful for evaluating possible structural abnormalities or to help detect complications or comorbid conditions, such as sinusitis or adenoid hypertrophy.

A 3-view sinus series (Caldwell, Waters, and lateral views) can be helpful in evaluating for sinusitis of the maxillary, frontal, and sphenoid sinuses. The ethmoid sinuses are difficult to visualize clearly on x-ray films. Plain x-ray films can be helpful for diagnosing acute sinusitis, but CT scanning of the sinuses is more sensitive and specific. For chronic sinusitis, plain x-ray films are often inconclusive, and CT scan is much preferred.

A lateral view of the neck can be helpful when evaluating for soft tissue abnormalities of the nasopharynx, such as adenoid hypertrophy.

CT

Coronal CT scan images of the sinuses can be very helpful for evaluating acute or chronic sinusitis. In particular, obstruction of the ostiomeatal complex (a confluence of drainage channels from the sinuses) can be seen quite clearly. CT scanning may also help delineate polyps, turbinate swelling, septal abnormalities (eg, deviation), and bony abnormalities (eg, concha bullosa).

MRI

For evaluating sinusitis, MRI images are generally less helpful than CT scan images, largely because the bony structures are not seen as clearly on MRI images. However, soft tissues are visualized quite well, making MRI images helpful for diagnosing malignancies of the upper airway.

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Other Tests

Nasal cytology

A nasal smear can sometimes be helpful for establishing the diagnosis of allergic rhinitis. A sample of secretions and cells is scraped from the surface of the nasal mucosa using a special sampling probe. Secretions that are blown from the nose are not adequate. The presence of eosinophils is consistent with allergic rhinitis but also can be observed with NARES. Results are neither sensitive nor specific for allergic rhinitis and should not be used exclusively for establishing the diagnosis.

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Procedures

Rhinoscopy

While not routinely indicated, upper airway endoscopy (rhinolaryngoscopy) can be performed if a complication or comorbid condition may be present. It can be helpful for evaluating structural abnormalities (eg, polyps, adenoid hypertrophy, septal deviation, masses, foreign bodies) and chronic sinusitis (by visualizing the areas of sinus drainage).

Nasal provocation (allergen challenge) testing

This procedure is essentially a research tool and is rarely indicated in the routine evaluation of allergic rhinitis. The possible allergen is inhaled or otherwise inoculated into the nose. The patient can then be monitored for development of symptoms or production of secretions, or objective measurements of nasal congestion can be taken. Some consider this test the criterion standard test for the diagnosis of allergic rhinitis. [53] However, it is not a practical test to perform routinely, and only an appropriately trained specialist should perform this test.

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