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Food Allergy: Joint Task Force Guidelines for Diagnosis and Management

Food Allergy: Joint Task Force Guidelines for Diagnosis and Management

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Food Allergy

Joint Task Force Guidelines for Diagnosis and Management

  

Contents:

Introduction

Clinical Background  - Figure

Individuals Suitable for Testing

Test Availability - Table 1

Interpretive Information - Table 2

Patient Management

References
 

Introduction [return to contents]

Guidelines for diagnosis and management of food allergy have been developed by the Joint Task Force on Practice Parameters representing the American Academy of Allergy, Asthma, and Immunology; the American College of Allergy, Asthma, and Immunology; and the Joint Council of Allergy, Asthma and Immunology.1,2 Here we provide a summary of these guidelines with a particular focus on the use of laboratory testing for the diagnosis and management of food allergy (IgE-mediated). It is important to bear in mind, however, that the majority of adverse reactions to food are not caused by IgE-mediated allergies. Refer to the complete Practice Parameter3 for more information on the differential diagnosis of non-IgE-mediated adverse food reactions.

Clinical Background [return to contents]

 It is important to diagnose food allergies to avoid unnecessary dietary restrictions that could negatively affect quality of life, nutritional status, and, in children, growth. The diagnostic algorithm developed by the Joint Task Force (Figure) begins with a relevant clinical history provided by the patient. This includes a list of suspected foods and the amount consumed, the time between ingestion and reaction, the type and duration of symptoms, repeatability of the reaction to the suspect food, requirement for cofactors (eg, exercise), and the time from last reaction. The second step is performance of a relevant physical examination including inspection of the upper and lower respiratory tract and the cutaneous and gastrointestinal (GI) systems. Third, determine if clinical and physical findings are consistent with an IgE-mediated reaction, which is characterized by a short time (ie, usually within minutes, rarely up to a few hours) from ingestion of the food to symptom onset, a severe reaction resulting from small amounts of food, an adverse reaction occurring with reexposure, and symptoms of pruritus, urticaria or angioedema, GI disturbance, rhinoconjunctivitis, bronchospasm, and anaphylaxis. Fourth, perform food-specific IgE testing when the history is consistent with an IgE-mediated food reaction. In vivo or in vitro tests can be used. Finally, perform an oral food challenge or trial elimination diet as indicated by food-specific IgE test results and clinical symptoms (see Figure)

Figure. Diagnosis and Management of Food Allergy. 1

Individuals Suitable for Testing [return to contents]

Testing is recommended for individuals who have a history consistent with an IgE-mediated food reaction as described above.

Test Availability [return to contents]

Available tests include food-specific IgE tests such as in vivo skin scratch, prick, or puncture tests (percutaneous) and in vitro (serum) tests (eg, ImmunoCAP®, AlaSTAT, HY-TEC) as well as oral food challenge tests and a trial elimination diet. The Joint Task Force does not recommend in vivo intracutaneous tests for the diagnosis of food allergy, citing insufficient evidence and higher risk of anaphylaxis.

In vivo food-specific IgE testing has a high negative predictive value (≥95%) but a low positive predictive value (≤50%). These tests are useful, therefore, as an initial test to rule out an IgE-mediated reaction to a highly suspected food..

In vitro IgE tests have roughly the same sensitivity and specificity as in vivo IgE tests and consequently have the same clinical application. In vitro tests are especially useful when skin tests are contraindicated, such as when the patient has a high risk of anaphylaxis from skin testing, has a widespread skin condition, or is receiving medications that affect skin test results. Radioimmunoassay procedures (radioallergosorbent test [RAST]) are no longer used. Current methods use a food-specific allergen bound to a solid phase to detect IgE in the patient’s serum. World Health Organization-based standards are used to quantify results, which are reported in kIU/L.

Oral food challenge tests and trial elimination diets (Table 1) may lead to or confirm a diagnosis of food allergy and may be useful for patient management.

Table 1. Non-cutaneous In Vivo Tests Used in Diagnosis and Management of Food Allergya

Food Challenge

Test

Definition Advantages Disadvantages

Open challenge

Uses either suspect
food in its natural form
or a placebo; not blinded
to patient or physician

Simplest to perform;
best when several foods
are suspect

Subject to patient and
physician bias; positive
result may require
blinded confirmation
testing

Oral challenge

Single-blind

Uses either suspect
food (given in gradually
increasing amounts) or
a placebo disguised
and blinded to the patient;
reactions are judged by
patient and physician

Eliminates patient bias
and need for test
interpreter to be blinded;
offers protocol flexibility

Test interpreter
potentially biased

Double-blind

Uses either suspect
food (given in gradually
increasing amounts) or
a placebo disguised and
blinded to the patient and
the physician; reactions
are judged independently
by patient and physician

Gold standard for
diagnosis of food allergy

Requires a third person
to prepare the blinded
food

Trial elimination

diet

Eliminates suspected
foods from the diet for
several weeks and then
gradually reintroduces
them one at a time with
reactions observed

Best when symptoms
are chronic; replaces
individual food
challenges when
several suspect foods
have been identified

Positive result requires
compelling supportive
evidence for a definitive
diagnosis

a Anaphylaxis is a risk and thus food challenges should be performed where emergency treatment is readily
available.

Interpretive Information [return to contents]

A negative food-specific IgE test result generally indicates lack of an IgE-mediated food reaction and probable tolerance of the food. However, results may be affected by the patient’s age, the reagents used, and the testing techniques used. For example, tests that use extracts from foods with stable proteins (eg, peanut, milk, egg, tree nuts, fish, and shellfish) are more reliable than those that use extracts from foods with labile proteins (eg, some fruits and vegetables). In vitro and in vivo skin tests use purified antigen that may differ from food challenge antigen that is raw, cooked, or otherwise processed, resulting in seemingly inconsistent results. Furthermore, in vivo skin tests are affected by the skin test devices used, the location of test placement, and the mode of measurement. In the event of a severe reaction and a negative test result, an open food challenge may be appropriate to rule out a food allergy. Preparation for a possible anaphylactic response should be made prior to the food challenge.

A positive food-specific IgE test result in a patient with a history of anaphylactic response to that food is considered diagnostic. There is no need for further testing.

Since a positive test alone does not necessarily indicate that ingestion of the food will result in a clinical response, further testing is required (Figure) in patients without an anaphylactic response to rule out cross-reacting proteins or other causes of a false-positive result (eg, eosinophilic gastroenteropathy). A larger in vivo skin test response size or greater concentration of IgE correlates with a greater likelihood of a clinical reaction to the food, but does not correlate with the type or severity of that reaction.

Interpretation of these and other available diagnostic tests is summarized in Table 2.

Table 2. Interpretation of Tests Used for Diagnosis of Food Allergy

Tests Positive Test Results Negative Test Results
Food-specific IgE testing

With history of anaphylaxis:
diagnostic; no further testing
needed

Tested foods are likely to be
tolerated (negative predictive
value ~95%)

Without history of anaphylaxis:
suggestive, but not diagnostic;
further testing needed

Consider open challenge in
some cases with severe
reaction

Open oral food challenge

Reaction is suggestive of food
allergy, but results are prone to
bias

Tested foods are likely to be
tolerated

Single blind oral food challenge

Reaction is suggestive of food
allergy, but results are prone to
bias

Tested foods are likely to be
tolerated irrespective of food
specific IgE test results

Double blind oral food challenge

Reaction is highly suggestive of
food allergy

Tested foods are likely to be
tolerated irrespective of food
specific IgE test results

Trial elimination diet Food allergy is probable when
chronic symptoms resolve
Perform oral challenge when
chronic symptoms persist

Patient Management [return to contents]

The following steps may be taken when managing a patient with a food allergy. First, educate and advise the patient to avoid the specific food allergen. Educational topics include how to read food labels, including an awareness of risk imposed by unfamiliar terms and cross-contamination during food processing; available dietary alternatives, including supplements; and how to avoid unintentional food allergen exposure (eg, in schools or restaurants). Second, educate and advise the patient on treating an anaphylactic response (eg, use of injectable epinephrine with or without antihistamine and seeking medical care for a systemic reaction). Third, perform periodic testing to determine newly-developed tolerance.

Avoidance of the food allergen may lead to future tolerance. Additionally, children are likely to outgrow some types of food allergies (eg, cow’s milk, wheat, and egg). A subsequent negative food-specific IgE test is likely to indicate tolerance to the food; however, a positive test is inconclusive since these tests may remain positive even when the patient no longer has clinical symptoms. An oral food challenge may be helpful in determining current tolerance status.

References [return to contents]

  1. Joint Task Force on Practice Parameters. Food allergy: a practice parameter. Ann Allergy Asthma Immunol. 2006;96:S1-S68.

  2. Boyce JA, Assa’ad A, Burks AW, et al. Guidelines for the diagnosis and management of food allergy in the United States: report of the NIAID-sponsored expert panel. J Allergy Clin Immunol. 2010;126:S1-S58.

  3. Bernstein IL, Li JT, Bernstein DI, et al. Allergy diagnostic testing: an updated practice parameter. Ann Allergy Asthma Immunol. 2008;100(Suppl 3):S1-S148.

Content reviewed 04/2013
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