Finding a Path to Safety in Food Allergy Assessment of the Global Burden, Causes, Prevention, Management, and Public Policy (2017) / Chapter Skim
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4 Assessments, Diagnostic Testing, Disease Monitoring, and Prognosis
4 Assessments, Diagnostic Testing, Disease Monitoring, and Prognosis
Pages 97-138
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From page 97... ...
. One of the major issues in food allergy is the common misconception that having a "positive test," by a blood test or allergy skin prick test (SPT, otherwise known as sensitization, or a condition in which an individual produces detectable food-specific immunoglobulin E [IgE]
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From page 98... ...
. The primary tools currently available for diagnosis include the medical history, elimination diets, SPT, food-specific IgE (sIgE)
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Symptoms can include skin symptoms of itchy rashes, hives, or swelling; eye symptoms of itching, tearing, redness, or swelling; oral symptoms of itching or swelling of the lips, tongue, or palate; upper airway symptoms of congestion, itching, sneezing, nasal discharge, or hoarseness; lower airway symptoms of cough, chest tightness, wheezing, or trouble breathing; gastrointestinal symptoms of nausea, pain, vomiting, or diarrhea; cardiovascular symptoms of fast or slow heart rate, dizziness, low blood pressure, confusion, loss of consciousness; uterine contractions; and a sense of "impending doom." Food allergy diagnostic testing also may be warranted for infants, young children, and selected older individuals with moderate to severe atopic dermatitis because a higher rate of food allergy occurs in these populations, whether or not the food allergy may be contributing to the rash (Boyce et al., 2010; Sidbury et al., 2014)
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From page 100... ...
, the authors concluded that testing for food allergy in siblings without a history of clinical reactivity appears to be unjustified and that screening may lead to negative consequences related to potential misdiagnosis and unnecessary avoidance of a food. MECHANISMS OF FOOD ALLERGY IN RELATIONSHIP TO DIAGNOSTIC TESTING Chapter 2 described specific food allergic disorders and pathophysiology.
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From page 101... ...
applicable to additional test selection and interpretation on a patient-specific basis, as will be reviewed further below. Elimination Diets Elimination diets, with removal of one or a few specific foods, is considered useful in diagnosing food allergy, especially for disorders with chronic symptoms, such as eosinophilic esophagitis (EoE)
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From page 102... ...
. Skin Prick Tests Guidelines recommend using SPTs for assistance in diagnosing IgEmediated food allergies, but the test results alone are not considered sufficient for diagnosis (Boyce et al., 2010; Muraro et al., 2014; Sampson et al., 2014)
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From page 103... ...
noted that predictive values vary between studies, likely for numerous reasons including patient selection, food challenge protocols, reagents used for testing, and manner of reporting. Food-Specific Serum IgE Guidelines recommend using sIgE tests to identify foods that may provoke IgE-mediated reactions, but the test result alone is not considered sufficient for diagnosis (Boyce et al., 2010; Muraro et al., 2014; Sampson et al., 2014)
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61% (95% CI: 47%-74%) NOTE: CI = confidence interval; SPT = skin prick test.
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A World Allergy Organization expert panel report suggests these tests as a third line approach following clinical history and extract-based testing, but that they may be included in second line testing for experienced users (Canonica et al., 2013)
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, and authors concluded that Ara h 2 testing should replace the other tests in clinical practice, especially in children. Although some disagreement may exist, various studies have determined that increasing levels of IgE against Ara h 2 correlates with risk of clinical reactivity (undetectable Ara h 2 does not exclude peanut allergy)
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From page 107... ...
Oral food challenges also can be performed in a single-blind protocol with the food masked from the patient's perspective so less patient bias occurs because of anxiety. Bias is a concern with OFC because anticipation of a reaction can result in subjective symptoms (e.g., abdominal pain, nausea, or eczema flare)
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Immediate symptoms typically occur within 2 hours after ingestion, but increases in atopic dermatitis symptoms may occur over hours or days. Rigorous objective criteria for determining tolerance or reactivity, consistent application of procedures, and good record keeping and documentation are paramount.
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MODALITIES NOT RECOMMENDED FOR ROUTINE USE Atopy Patch Test The atopy patch test (APT) is performed in a manner similar to patch testing that is routinely used to evaluate allergic contact dermatitis, except that foods are used.
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summarized the results from seven studies, with negative predictive values of more than 90 percent and only 50 percent for milk, and variable positive predictive values. They suggested the APT (along with SPT and sIgE)
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The diagnostic value of the ratio was not better than for sIgE alone. In contrast, another study looking at the ratio evaluated 195 OFCs among 161 children, and found that the ratio was more informative than sIgE alone for peanut, tree nuts, seeds, and shellfish but not milk, egg, wheat, or soy (Gupta et al., 2014)
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. The position paper also reviewed the use of BAT to predict development of tolerance in food allergic children (N=4 studies)
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From page 113... ...
while binding to Ara h 2 is associated with systemic peanut allergy. However, on an individual patient or research study participant basis, degree of binding to Ara h 2 does not appear to accurately predict severity (Astier et al., 2006; Klemans et al., 2013a,b; Leo et al., 2015; Peeters et al., 2007)
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. Most children with allergies to cow milk, egg, soy, and wheat will develop tolerance by adulthood, whereas resolution of peanut, tree nut, and seafood allergies is less likely (less than or equal to 20 percent)
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Testing based on the initial impressions is conducted and interpreted based on the results of the history and suspected foods and related pathophysiology. This may include tests for IgE, elimination diets and/or OFCs, depending on the circumstances.
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. Additionally, it may be possible to isolate a number of factors from the medical history and simple diagnostic tests to estimate the risk of an allergy, using a standardized approach, but this also needs validation (DunnGalvin et al., 2011)
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Guidelines suggest considering tests for foodspecific IgE and APT to help identify causal foods, specifically for evaluating EoE (Boyce et al., 2010; Sampson et al., 2014)
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For example, a large proportion of individuals with peanut allergy will test positive to
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Although the test rate of cross reactivity is higher than the observed rate of clinical cross reactivity, studies on this topic are limited and likely reflect results that vary depending upon methodology, patient selection, and geographic influences, including pollen sensitization. Estimated rates of clinical cross reactivity among crustacean shellfish is 38 percent, among fish 30 to 75 percent, among tree nuts 12 to 37 percent (varies depending on the nuts; for example, walnut and pecan are more similar, cashew and pistachio are more similar)
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A case can be made for evaluating specific allergens associated with these syndromes, such as gliadin and lipid transfer proteins in some settings, but the diagnostic utility is not fully understood (Muraro
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performed genomewide DNA methylation profiling on subjects who had undergone OFC, concurrent SPTs, and specific IgE tests (Martino et al., 2015)
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As reviewed in the discussion above, food allergy testing strategies (history, diagnostic elimination diet, OFC, SPT, sIgE, CRD, APT) are generally not well standardized, including the various factors involved with the history, elimination diets, and food challenge.
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From page 123... ...
Although this process often may include an initial evaluation by a primary physician, it is important that those with suspected food allergy be diagnosed appropriately, which is likely to involve referral to or consultation with a physician specialist who can diagnose, comprehensively evaluate, and manage the food allergy. Food allergy evaluation procedures include a medical history and physical examination, and also may include food-specific skin prick test, food-specific serum immunoglobulin E test, diagnostic food elimination diet, and oral food challenge (OFC)
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From page 124... ...
have limitations that can result in misdiagnosis, primarily overdiagnosis, requiring procedures such as OFCs to confirm a proper diagnosis. For example, currently available, simple diagnostic tests that are often used to diagnose IgE-mediated food allergies, the sIgE test and SPT, actually diagnose sensitization, not food allergy.
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Eur Ann Allergy Clin Immunol 46(4)
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J Allergy Clin Immunol 134(2)
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From page 127... ...
ratios in egg allergy. J Allergy Clin Immunol 129(3)
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J Allergy Clin Immunol Pract 3(5)
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J Allergy Clin Immunol Pract.
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J Allergy Clin Immunol Pract 2(5)
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2013. The utility of peanut components in the diagnosis of IgE-mediated peanut allergy among distinct populations.J Allergy Clin Immunol Pract 1(1)
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J Allergy Clin Immunol Pract 3(6)
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From page 133... ...
. J Allergy Clin Immunol 106(5)
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J Allergy Clin Immunol Pract 4(2)
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J Allergy Clin Immunol 130(2)
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-- allergic individuals suffering from allergic reactions to raw fruits and vegetables. J Allergy Clin Immunol Pract 1(6)
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Curr Opin Allergy Clin Immunol 7(3)
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