A simple new blood test for allergy triggers

Virtually every guideline from allergy and asthma organizations stresses avoidance of disease triggers.1,2 In the case of asthma and allergic rhinitis, this may mean avoiding dust mites, ragweed, or a host of other potential triggers. Traditionally, clinicians have either made educated guesses regarding triggers or have simply focused on treating the disease both on a chronic basis and when acute exacerbations occur. Now a new IgE-specific blood test adds objective evidence to the diagnosis of patients with allergy symptoms. This in vitro quantitative assay measures allergenspecific IgE in human serum and is best used in conjunction with other findings gathered during a history and physical examination. With a single venipuncture, IgE-specific testing provides a clinically relevant means of confirming or excluding the presence of atopic disease in patients with viral or allergic respiratory symptoms, especially rhinitis and asthma. The test, which is both sensitive and specific, provides a quantitative measure of allergy and can be performed for many hundreds of allergens, such as weeds, trees, pollens, mold, and animal dander, as well as foods and food products.

Current IgE-specific antibody testing is very different from the first-generation radioallergosorbent test (RAST) that used IgE-binding (anti-IgE) antibodies labeled with radioactive isotopes to quantify the levels of IgE antibody in the blood. In addition to being expensive, RAST had significant flaws relating to both sensitivity and specificity, and allergy skin testing, whenever possible, remained the preferred method.

The newer IgE-specific methods now being advocated use colorimetric or fluorometric technology (ie, fluorescence enzyme immunoassay) in place of radioactive isotopes.3 IgEspecific testing utilizes a single tube of blood drawn in the office. The quantitative results, which are usually available in 2 to 3 days, will indicate specific substances to which the patient is allergic, how allergic the patient is on a scale of 1 to 5, and if the patient has a total IgE response but no response to common allergens. This last finding should trigger a broader search for specific allergens. Results are easily interpreted with a brief review available on the manufacturer's Web site (www. isitallergy.com/). Allergy profiles provided on the Web site list approximately 95% of the most common respiratory and/or food allergens and are individualized for specific geographic regions.4 If a patient's total IgE level is high but common allergy testing does not uncover a specific etiology, further investigation with more specific tests for carefully chosen allergens is often warranted because studies have shown that patients with an elevated total IgE have a high probability of allergic sensitization. IgE tests are highly sensitive and specific. They are considered equivalent—and may in some instances be superior— to skin testing (see “Figure. Comparison of allergy testing modalities” in the online version of this article).5

IgE-specific blood testing has certain advantages over skin testing beyond availability in a primary care setting.6 IgE-specific testing would be preferred when the patient takes medications, such as antihistamines or corticosteroids, that can interfere with other tests and the discontinuation of those medications is undesirable or contraindicated. IgE testing can also be used when patients suffer from severe skin conditions, such as widespread eczema or psoriasis. Lastly, unlike skin testing, serum testing can also be used without any risk when a patient is so highly sensitive to suspected allergens that administration of those allergens might result in potentially serious side effects, such as anaphylaxis.

There are at least three specific instances in which you may wish to incorporate IgE-specific testing into your practice and particularly in the pediatric patient with certain childhood diseases. IgE-specific testing can answer three questions: (1) Are the patient's symptoms caused by atopy? (2) Which allergens are responsible? (3) Where is the patient on the food/inhalant sensitization continuum, also known as the allergic march? Typical childhood diseases that may benefit from further studies include eczema, GI distress, recurrent acute otitis media, rhinitis, or asthma. If IgE-specific test results are negative, the symptoms are unlikely to have an underlying atopic basis and should be managed with symptomatic treatment. If IgEspecific test results are positive, other treatment alternatives become possible, along with allergen avoidance.

The second instance for possible use of IgE testing is in patients with upper respiratory tract disease, such as rhinitis. IgE-specific testing will help determine if symptoms are consistent with allergic rhinitis or another etiology, such as vasomotor rhinitis, which would warrant different treatment. In upper respiratory tract disease, positive IgE-specific results indicate atopy, but quantitative results for the most common allergens give a clearer understanding of the major and minor contributors. Although not all allergens produce the same degree of response and each person's immune system responds differently, the quantitative scores typically reflect severity of allergen impact. With the knowledge provided in IgE-specific results, clinicians can direct patients to implement specific and detailed environmental controls. Eliminating the major offending groups of allergens may be important because of the cumulative threshold response of allergic disease.

The final instance in which IgE testing may be considered is asthma in all its variations. Successful management of asthma commonly depends on distinguishing between allergic and nonallergic disease and accurately identifying a patient's symptom triggers. In allergic asthma, allergic sensitivities play a critical role in disease onset and severity. Patients commonly have a history of atopic disease, and their asthma exacerbations are triggered by environmental allergens. Some 60% of adult patients and up to 90% of children with asthma are estimated to have allergic asthma. Regardless of the different etiologies, these conditions share three common confounding symptoms: cough, wheezing, and dyspnea. Experts increasingly support the one airway theory, which holds that a common inflammatory process links upper and lower airways. In addition, more and more recommendations call for persons with asthma to be evaluated for signs and symptoms of persistent allergic rhinitis and vice versa. For the first time, IgE-specific testing is available in virtually every setting and can assist in definitive treatment with respect to the first step in allergy triggers and avoidance of those triggers.

Despite our increasing ability to accurately identify allergic triggers, patients likely will not be able to avoid all their allergens. The good news is they don't have to. They simply need to move below their allergic threshold (see Figure 1). Regardless of their allergic disease (ie, allergic rhinitis, asthma, eczema, etc.), few patients have a single allergic trigger. Instead patients have multiple triggers that “stack” up on one another until the individual reaches his or her allergic threshold and develops symptoms. By avoiding some or most of their triggers, patients may be able to slip below their allergic threshold so that their symptoms may largely disappear or at the very least become more easily managed. JAAPA