Evaluation and treatment of the patient with allergic rhinitis

Diagnostic tests include skin prick testing, intradermal testing, and in vitro blood tests. Nasal challenge testing, nasal smears, sinus transillumination, and nasopharyngoscopy are nonspecific tests. They are not recommended for routine evaluation but may be useful in selected cases when allergen-specific tests have failed to clarify the cause of the rhinitis. An expert panel has stated that no studies address the cost-effectiveness of any of these methods.²

Skin prick testing (SPT) is considered the most convenient and least expensive screening test. SPT can detect IgE antibodies in patients with reliable exposure histories.¹³ Sensitivity and specificity are difficult to determine, for a number of reasons. First, as previously mentioned, there is no clearly defined reference standard.¹¹ Second, only 5 allergen extracts have been standardized for defined quantities known to induce biologic activity. Standardized extracts in the United States include ragweed pollen, cat dander, house dust mites, Hymenoptera venoms, and some grasses. All other extracts are local or regional preparations, and skin tests with nonstandard extracts are not necessarily reproducible.¹¹ Third, even with a single individual, there can be wide variation in skin reaction to the same reagent, depending on the device used.¹⁴ As a result, correlation between SPT and inhalation challenges vary from 60% to 90%.¹³

Intradermal skin tests (IDST) are usually done when SPT yields a negative result despite a history compatible with allergic rhinitis.¹³ The primary advantage of IDST is sensitivity afforded by a fixed concentration of allergen. Because of this sensitivity, not all reactions are clinically relevant.¹³ In fact, IDST is often used as a reference standard in studies of the accuracy of SPT and in vitro tests.

Several in vitro assays of specific IgE antibodies are available. They are all modeled after the original radioallergosorbent tests (RAST); the term “RAST” is often used interchangeably with any type of in vitro blood test.¹³ IgE antibody tests have a high false-positive rate, meaning the test is positive in patients without allergy symptoms. RAST tests are less sensitive than SPT, with a mean sensitivity of 75% and a range of approximately 50% to 95%.¹³

The 3 primary diagnostic tests for allergic rhinitis are usually compared with each other and not to a recognized standard. Table 1 summarizes data from a study that compared all 3 tests with subjects who were placed in a small room with 2 cats and their bed.¹² While this is one of very few studies that contrasts all 3 tests to a reasonable reference standard, the findings cannot necessarily be extrapolated to other airborne allergens.

In the hope of limiting referrals to allergists for testing, and reducing the uncertainty in making a diagnosis, one study looked at the RAST response to 19 allergens. The authors found that of all the patients who responded to any allergen, 95% exhibited responses specifically to grass pollen, dust mites, or cat dander. They went on to conclude that 96.3% of patients with allergic disease could be correctly identified with a combination of a standardized history (available in the study text), a total serum IgE of greater than 40 U/mL, and in vitro tests for cat dander, dust mites, and grass pollen.¹⁵

TABLE 1

Accuracy of diagnostic tests for diagnosis of cat allergy¹³

Treatment

Untreated allergic rhinitis can have a significant impact on quality of life. Patients are bothered by nose blowing, disrupted sleep, fatigue, and decreased concentration.¹ In one 1996 survey, 32 % of patients said that allergy attacks embarrassed them or interfered with their quality of life.¹⁶ As a result, most patient-oriented studies on treatment evaluate the impact on health-related quality of life.¹⁷

The initial form of treatment is usually avoidance of the allergen, although this can be difficult. For animal allergens, washing pets and using high-efficiency particulate air (HEPA) filters have been shown to temporarily reduce the volume of airborne allergens but not to improve patient-oriented outcomes.^18,19 Removing the pet from the home is the only sure remedy.¹⁸ More studies are needed to evaluate the benefit of multiple home treatments to reduce exposure to cockroach and fungal allergens.¹⁸ A systematic review of several studies showed that maternal antigen avoidance during lactation reduced the incidence of atopic dermatitis in at-risk infants.²⁰ A meta-analysis of measures to avoid house-dust mites showed no clear benefit for patients with asthma¹⁰ It is unclear if these findings can be extrapolated to other atopic conditions such as allergic rhinitis.