Tests and Diagnosis for Allergies
Proper diagnosis of allergy begins with a thorough medical history and physical examination. When a relationship between specific allergen(s) and symptoms is suspected, allergy tests can be performed to identify the specific allergenic substance(s) and treat the symptoms.
Scratch or skin prick test: This is the most commonly used allergy test. During this test, small amounts of suspected allergens are introduced on normal skin on the forearm or on the upper back using a small prick or needle. Redness, itching, and a raised wheal (welt) appear within 20 minutes if there is a positive reaction to an antigen. A common side effect is itchiness or hives around the wheal. Because it involves introduction of possible allergens, it does carry some risk, including the rare but serious occurrence of a life-threatening anaphylactic reaction.
Radioallergosorbent test (RAST): This test evaluates the levels of specific IgE antibody and activity in serum. Like the skin test, the RAST provides allergen-specific information. The patient provides a blood sample at a clinic or laboratory. Because it is performed in the lab on serum only, there are no risks associated with this test. Common side effects are related to giving blood, such as minor pain or slight bruising.
Enzyme linked immunosorbent assay (ELISA): The ELISA is another method used to measure various levels of IgE. It provides an indirect determination of what materials a person may be allergic to. Like RAST, it carries no direct risk to the patient.
Differential leukocyte count: The white blood cell count and differential is part of the complete blood count (CBC). The total number and types of white blood cells are measured. They generally include neutrophils, lymphocytes, monocytes, basophils, eosinophils, and bands. Eosinophils are often elevated with allergic reactions (Fischbach 1996). This test is nonspecific and provides no information about specific allergenic substances.
Elimination-challenge diet: The elimination-challenge diet is useful for detecting food allergies, but is very difficult to follow and requires diligence. This diet involves removal of common allergenic foods for at least two weeks; typically wheat, corn, soy, dairy, etc. Overly processed foods, food dyes, and spices may also be eliminated. The patient then remains cognizant of symptoms for several weeks and slowly continues removing select food items until all the symptoms of allergy disappears. The elimination diet is followed by a systematic reintroduction of possible triggers to the diet, one at a time, until symptoms reappear. Symptoms should be closely monitored (Rolinck-Werninghaus 2005).
Pharmacologic Treatments for Allergy
Once an allergen has been identified, conventional therapy relies on avoidance of the allergen whenever possible and a diverse group of pharmaceuticals. The most common pharmaceuticals include the following:
Antihistamines. This group of pharmaceuticals blocks the effect of histamine and reduces the signs and symptoms of asthma and allergy. Oral antihistamines can be used to treat nasal symptoms including congestion, sneezing, itchy or runny nose and itchy, watery eyes. Antihistamines may also control skin flares and itching, and smooth muscle constriction in the lungs which produces wheezing and aggravates asthma. Some antihistamine drugs may cause drowsiness and loss of coordination. Antihistamines are to be avoided in patients with high blood pressure or narrow angle glaucoma.
Decongestants. These drugs cause small arterioles to constrict and decrease fluid and mucous secretion. Decongestants may be oral medications, nasal sprays, or eye drops. Active ingredients include pseudoephedrine, desoxyephedrine, oxymetazoline, and phenylephrine. Over-the-counter decongestants are frequently sold in combination products with antihistamines. Side effects may include increased blood pressure, arrhythmia, heart attack, anxiety, and dizziness.
Glucocorticosteroids. These anti-inflammatory medications are taken orally, topically, inhaled into the lungs, or taken in nasal sprays. Intranasal corticosteroid sprays are used to treat allergic and non-allergic rhinitis with a minimal risk of systemic adverse effects. Relief can be expected after 7-8 hours of dosing but it may take 2 weeks before the drug becomes maximally effective. Inhaled corticosteroids are typically used as treatment in persistent moderate to severe asthma. It can reduce symptoms, decrease airway hyperresponsiveness and inflammation and improve lung function. Topical corticosteroids are used to treat eczema. They are an effective first-line treatment, but they can inhibit the repair of skin cells and interfere with recovery in the long term (Pawankar 2011). Side effects can be serious if corticosteroids are taken orally over a long period of time.
Leukotriene antagonists. Leukotrienes are generated in mast cells and other white blood cells and contribute to the allergic response. Leukotriene antagonists are designed to inhibit leukotriene formation and are used to treat seasonal allergic rhinitis and mild persistent asthma.
Cromolyn sodium. Cromolyn is used as a nasal spray for rhinitis and inhaled for asthma and bronchospasm. It works by stabilizing mast cell membranes, preventing them from releasing histamine. It can prevent allergic rhinitis if used before symptoms start. However, cromolyn has fallen out of favor as a primary treatment option due to an inconvenient dosing regimen requirement (it must be taken four times daily) and the advent of effective, long-acting medications such as leukotriene receptor antagonists.
Beta-agonists. These are drugs that selectively activate beta-1- and beta-2-adrenergic receptors, causing smooth muscle relaxation and bronchodilation. There are two kinds of beta-agonists: long-acting B2-agonist (LABA) and short-acting B2-agonist (SABA). In combination with inhaled corticosteroids, LABAs improve symptoms, decrease nighttime asthma and reduce the number of exacerbations (Pawankar 2011). SABAs can rapidly dilate the airways and improve breathing during an asthma attack. SABA should only be used as needed to reduce the risk of adverse side effects. The most common associated with bronchodilators include nervousness, restlessness and trembling. Albuterol and epinephrine are included in this category.
Immunotherapy. Allergen-specific immunotherapy involves a gradual desensitization of the immune response. The patient receives increasing amounts of the specific antigen to induce the immune system to produce protective antibody. Treatment may be continued for three or more years. It is the only treatment that can reduce symptoms related to allergic rhinitis over time although there is a risk of side effects because of allergic reaction to the antigen that is intended to be therapeutic.
In the United States, immunotherapy is most frequently as a subcutaneous injection. However, European physicians have employed another form of immunotherapy for decades – sublingual immunotherapy or “allergy drops”. (Lin 2011).
Sublingual immunotherapy, in which small doses of allergen are delivered in a diluted solution under the tongue, works in the same way injectable immunotherapy does. Several comprehensive reviews have shown that sublingual immunotherapy is effective for reducing symptoms associated with allergic conditions including allergic rhinitis and allergic conjunctivitis (Calderon 2011; cox 2011). Moreover, sublingual immunotherapy appears to be associated with fewer systemic reactions (Bahceciler 2011). Data indicate that sublingual immunotherapy may be an alternative for those at high risk for anaphylactic reactions or those who do not wish to receive an antigen injection.
Use of Probiotics
In order to prevent the development of childhood allergic diseases, an infant’s immune system must mature from a Th2- to a Th1-dominated response through microbial contact soon after birth. In comparison with the time before antibiotics and common presence of infectious diseases, along with the widespread use of antimicrobial agents in consumer products like soap, individuals in modern times have reduced contact with microbes. In the theory known as the “hygiene hypothesis”, scientists speculate that an antiseptic environment results in a lack of microbial stimulation to the gut immune system and causes an increase in allergic disease (Penders 2007; Pan 2010). In fact, studies have shown that non-allergic children have higher levels of Bidifobacteria and Lactobacilli compared to allergic children (Kalliomaki 2001). The presence of these ‘harmless’ probiotic bacteria in the intestinal biota seem to correspond with protection against allergy.
As defined by the World Health Organization, probiotics are “live microorganisms which, when administered in adequate amounts as part of food, confer a beneficial health effect by producing gut microflora on the host” (WHO 2001).
Many randomized trials, clinical and experimental studies and meta-analyses have been conducted on the efficacy of probiotics on the treatment or prevention of allergic diseases.
Randomized controlled trials (RCTs) showed that using probiotics provided significant clinical benefits to children with allergic rhinitis. Heat-killed or live Lactobabillus casei decreased the frequency and severity of nose and eye symptoms and improved the quality of life for children who were sensitized to house dust mites (Wang 2004; Peng 2005). Among preschool children with seasonal allergic rhinitis, L. casei was also found to reduce symptoms and the number of episodes, and lessen the use of relief medications. The effect, however, was not statistically significant for asthma (Giovannini 2007). Similar positive effects were observed among children with pollen-sensitized allergic rhinitis who were treated with oral Bacillus clausii spores (Ciprandi et al, 2005).
Studies that examined the effects of probiotics at the level of the immune system also showed some positive effects. Supplementation with L. gasseri significantly reduced serum IgE specific to Japanese cedar pollen in children with seasonal allergies (Morita 2006).
Positive effects were also observed among patients who received Bifidobacterium longum BB536 supplement (Xiao 2006). Moreover, BB536 seems to suppress Th-2 cell attraction and activation, suggesting it may be effective in blunting the IgE-mediated allergic response (Iwabuchi 2009). In a 28-week clinical trial, BB536 favorably modulated intestinal microbiotia, lessening the burden of allergens, in subjects with cedar pollen allergies (Odamaki 2007). In an experimental model, a BB536 DNA oligodeoxynucleotide, shunted the cytokine profile in favor of Th1 and suppressed IgE levels, both markers of and contributors to a lessened allergic response (Takahashi 2006).
In two randomized controlled trials studying the clinical effects of L. plantarum No. 14 (LP14), eosinophil counts decreased immediately after intake in the group that took LP14, and the percentage of Th1 helper T cells increased after 6 weeks. LP14 also strongly induced the gene expression of Th1-type cytokines, indicating that probiotics are clinically effective in the management of seasonal allergic disease.(Nagata 2010).
A review of 13 randomized, controlled trials on the effectiveness of probiotics in the treatment or prevention of atopic dermatitis found that, regardless of IgE sensitization, Lactobacillus rhamnosus GG (LGG) and other probiotics were effective in preventing AD. Probiotics also reduced the severity of AD in half of the trials evaluated, although there was no significant change observed in the inflammatory markers (Betsi 2008). One study demonstrated that skin severity scores were significantly lower in group given heat-killed L. paracasei, and the placebo group used nearly double the amount of topical medicine during the study period (Moroi 2011). Similar positive results were observed among preschool children with moderate to severe AD who were treated with a supplemental probiotics mixture. The absolute counts and percentages of CD lymphocyte subsets in the peripheral blood also decreased in the probiotic group (Gerasimov 2010).
On the other hand, a randomized trial showed that prenatal treatment with LGG was not sufficient to prevent eczema among infants in the first year of life (Boyle 2011).
In terms of preventing allergies, a meta-analysis of six studies reported significant benefits in infants at high risk of allergy who used probiotic supplements containing L. rhamnosus. A recent study (Berni 2011) demonstrated that infants with suspected cow’s milk allergy who were given partially hydrolyzed infant food supplemented with LGG had a higher probability of acquiring tolerance to cow’s milk protein at 6 and 12 months compared with infants who were not given LGG supplementation. In addition, skin patch test responses were negative in all infants who acquired tolerance.
Clinical improvements have been reported among patients with allergic rhinitis and IgE-sensitized atopic eczema, but studies on the efficacy of probiotics in the management of asthma remain inconsistent. Possible reasons include differences in study designs, types of probiotics used and duration of probiotic supplementation, which limits the comparability of results (Ozdemir 2010).