Differentials

Sinusitis, Acute
Sinusitis, Chronic

Other Problems to be Considered

Vasomotor rhinitis or nonallergic rhinitis
Gustatory rhinitis (vagally mediated)
Rhinitis medicamentosa (eg, due to topical decongestants, antihypertensives, cocaine abuse)
Hormonal rhinitis (eg, related to pregnancy, hypothyroidism, oral contraceptive use)
Anatomic rhinitis (eg, deviated septum, choanal atresia, adenoid hypertrophy, foreign body, nasal tumor)
NARES
Immotile cilia syndrome (ciliary dyskinesis)
Cerebrospinal fluid leak
Nasal polyps
Granulomatous rhinitis (eg, Wegener granulomatosis, sarcoidosis)

Lab Studies

• Allergy testing: 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. The physician needs 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 radioallergosorbent test (RAST), 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, RAST, 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 RAST).

       

    • As with skin testing, virtually all of the allergens that cause allergic rhinitis (see Causes) can be determined using the RAST, 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 RAST). 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.

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• 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.