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Allergy tests: what IgE tests show, and why IgG food panels do not diagnose allergy

How allergy is diagnosed, the difference between being sensitized and being allergic, what component tests add, and what allergy societies say about IgG food panels.

4 minute read13 sources, each checked word for wordLibrary checked October 18, 2026

In short

  • Diagnosis starts with an allergy-focused history, followed by tests for IgE sensitization such as blood specific IgE and skin prick tests.E2Good1
  • The reference standard for diagnosing food allergy is the oral food challenge.E2Good1
  • Most children labeled peanut-sensitized on standard tests do not have peanut allergy.E2Good2
  • A European task force concluded that IgG4 tests to foods should not be performed for food-related complaints. It also concluded that a positive result reflects exposure, not allergy.E2Good3

How sure each claim is:E1StrongE2GoodOfficial textReviewWhat the grades mean

How is a food allergy diagnosed?

European guidelines describe diagnosis as starting with an allergy-focused clinical history. Tests for IgE sensitization follow: serum allergen-specific IgE (sIgE), the skin prick test (SPT), and the basophil activation test (BAT) where it is available.E2Good1

The oral food challenge, in which the food is eaten in steps under supervision, is the reference standard. The guidelines describe it as needed when results are unclear, and open challenges suit most cases.E2Good1

An American allergy work group describes food challenges as an integral part of an allergist's practice. Challenges are used to show whether a person reacts to a food or not.E2Good4

Sensitized is not the same as allergic

A positive skin or blood test shows sensitization: the immune system has made IgE to the food. It does not always mean the food causes symptoms. In one study of children sensitized to peanut, only about 22% had clinical peanut allergy.E2Good2

British guidelines explain that a larger skin test or higher sIgE makes clinical allergy more likely. But the size of the result does not tell how severe a reaction would be.E2Good5

A 2024 review of test accuracy found that skin prick tests and sIgE to whole-food extracts are sensitive (they catch most true allergies). Tests to single components and the basophil activation test are specific (a positive result is more likely to be real).E1Strong6

Research has identified IgE levels that predicted reactions to egg, milk, peanut and fish with more than 95% certainty in children. The authors said these levels could spare many children a full challenge.E2Good7

What do component tests add?

Component tests measure IgE to single proteins inside a food. European guidelines name Ara h 2 from peanut, Cor a 14 from hazelnut and Ana o 3 from cashew as useful. They are especially useful in people sensitized to pollen.E2Good1

Ara h 2 was the most important predictor of clinical peanut allergy in one study.E2Good2

For wheat allergy triggered by exercise (wheat-dependent exercise-induced anaphylaxis), IgE to the wheat protein omega-5 gliadin identified 80% of patients. That was more than tests to whole wheat or gluten.E2Good8

What about IgG and IgG4 food panels?

Blood tests for IgG4 against hundreds of foods are persistently promoted for diagnosing food reactions.E2Good3

A European Academy of Allergy and Clinical Immunology task force found that many people have positive IgG4 results with no symptoms from those foods.E2Good3

The task force concluded that food-specific IgG4 does not indicate food allergy or intolerance. It reflects a normal immune response after eating those foods, and the test should not be performed for food-related complaints.E2Good3

For nasal allergies, the 2020 US practice parameter states that food allergy testing is not recommended in the routine evaluation of rhinitis.E2Good9

Other tests people hear about

Tryptase. US practice parameters call measuring serum tryptase important for diagnosing anaphylaxis and for finding underlying mast cell disorders. European guidelines suggest taking blood for tryptase at the time of a suspected reaction.E2Good10,11

Celiac blood tests. Celiac disease is tested differently from allergy. Tissue transglutaminase IgA is a key blood test. Cutting down on gluten before testing is discouraged because it can make both blood tests and biopsies less sensitive.E2Good12

Mast cell activation syndrome. Experts note that overt MCAS is unusual. Many people referred for it turn out to have other diseases or allergic conditions that do not meet its criteria.E2Good13

What is not known yet

Test cut-offs differ by food and by age, and some foods have none: British guidelines note that cut-off values are not available for tree nuts.E2Good5

Questions you might bring to your clinician

  1. Does this result show sensitization only, or a confirmed allergy?
  2. Would a component test or a supervised food challenge add anything here?
  3. How does the size of this result relate to the chance of a reaction, and what can it not tell us?
  4. Is any test I was offered, such as an IgG panel, one that allergy guidelines support?

Every claim in this guide was written from its sources and checked against them word for word. Its clinical review by Dr. Recio, whose specialty is anesthesia, is pending; an allergist has not yet reviewed it. This line changes when each review is done.

Sources

Each source opens on PubMed, DailyMed or the publisher's page. Under each one are the exact words from it that this page relies on, copied word for word and checked against the original.

  1. EAACI guidelines on the diagnosis of IgE-mediated food allergy. Santos AF, Allergy, 2023. E2Good Guideline
    The words this page rests on
    Food allergy diagnosis starts with an allergy-focused clinical history followed by tests to determine IgE sensitization, such as serum allergen-specific IgE (sIgE) and skin prick test (SPT), and the basophil activation test (BAT), if available.
    The reference standard for food allergy diagnosis is the oral food challenge (OFC). OFC should be performed in equivocal cases. For practical reasons, open challenges are suitable in most cases.
    The measurement of sIgE to allergen components such as Ara h 2 from peanut, Cor a 14 from hazelnut and Ana o 3 from cashew can be useful to further support the diagnosis, especially in pollen-sensitized individuals.
  2. Allergy or tolerance in children sensitized to peanut: prevalence and differentiation using component-resolved diagnostics. Nicolaou N, J Allergy Clin Immunol, 2010. E2Good Observational study
    The words this page rests on
    The majority of children considered peanut-sensitized on the basis of standard tests do not have peanut allergy. Component-resolved diagnostics may facilitate the diagnosis of peanut allergy.
    We estimated the prevalence of clinical peanut allergy among sensitized subjects as 22.4% (95% CI, 14.8% to 32.3%).
    The peanut component Ara h 2 was the most important predictor of clinical allergy.
  3. Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report. Stapel SO, Allergy, 2008. E2Good Consensus statement
    The words this page rests on
    In conclusion, food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.
    Serological tests for immunoglobulin G4 (IgG4) against foods are persistently promoted for the diagnosis of food-induced hypersensitivity.
    However, many serum samples show positive IgG4 results without corresponding clinical symptoms.
  4. Conducting an Oral Food Challenge: An Update to the 2009 Adverse Reactions to Foods Committee Work Group Report. Bird JA, J Allergy Clin Immunol Pract, 2020. E2Good Consensus statement
    The words this page rests on
    Oral food challenges are an integral part of an allergist's practice and are used to evaluate the presence or absence of allergic reactivity to foods. A work group within the Adverse Reactions to Foods Committee of the American Academy of Allergy, Asthma & Immunology was formed to update a previously published oral food challenge report.
  5. BSACI guideline for the diagnosis and management of peanut and tree nut allergy. Stiefel G, Clin Exp Allergy, 2017. E2Good Guideline
    The words this page rests on
    The magnitude of a SPT or sIgE relates to the probability of clinical allergy, but does not relate to clinical severity. SPT of ≥ 8 mm or sIgE ≥ 15 KU/L to peanut is highly predictive of clinical allergy. Cut off values are not available for tree nuts.
  6. Systematic review and meta-analyses on the accuracy of diagnostic tests for IgE-mediated food allergy. Riggioni C, Allergy, 2024. E1Strong Meta-analysis
    The words this page rests on
    In conclusion, SPT and specific IgE to extracts had high sensitivity whereas specific IgE to components and BAT had high specificity to support the diagnosis of individual food allergies.
  7. Utility of food-specific IgE concentrations in predicting symptomatic food allergy. Sampson HA, J Allergy Clin Immunol, 2001. E2Good Observational study
    The words this page rests on
    However, in a retrospective analysis of children and adolescents with atopic dermatitis and food allergy, discrete food-specific IgE concentrations were established that could predict clinical reactivity to egg, milk, peanut, and fish with greater than 95% certainty.
    Quantification of food-specific IgE is a useful test for diagnosing symptomatic allergy to egg, milk, peanut, and fish in the pediatric population and could eliminate the need to perform double-blind, placebo-controlled food challenges in a significant number of children.
  8. Sensitivity and specificity of recombinant omega-5 gliadin-specific IgE measurement for the diagnosis of wheat-dependent exercise-induced anaphylaxis. Matsuo H, Allergy, 2008. E2Good Observational study
    The words this page rests on
    In patients with WDEIA, the sensitivities of the allergen-specific IgE tests for wheat, gluten, Pep A, Pep B and romega-5 gliadin were 48%, 56%, 76%, 22%, and 80%, respectively.
    Measuring the concentration of specific IgE antibodies to romega-5 gliadin is more useful than to wheat, gluten, or Pep A in the identification of patients with WDEIA.
  9. Rhinitis 2020: A practice parameter update. Dykewicz MS, J Allergy Clin Immunol, 2020. E2Good Practice parameter
    The words this page rests on
    Cough is emphasized as a common symptom in both AR and NAR. Food allergy testing is not recommended in the routine evaluation of rhinitis.
  10. Anaphylaxis: A 2023 practice parameter update. Golden DBK, Ann Allergy Asthma Immunol, 2024. E2Good Practice parameter
    The words this page rests on
    Diagnostic criteria for anaphylaxis have been revised, and patterns of anaphylaxis are defined. Measurement of serum tryptase is important for diagnosis of anaphylaxis and to identify underlying mast cell disorders.
  11. EAACI guidelines: Anaphylaxis (2021 update). Muraro A, Allergy, 2022. E2Good Guideline
    The words this page rests on
    The use of clinical criteria to identify anaphylaxis is suggested with blood sampling for the later measurement of tryptase.
  12. AGA Clinical Practice Update on Diagnosis and Monitoring of Celiac Disease-Changing Utility of Serology and Histologic Measures: Expert Review. Husby S, Gastroenterology, 2019. E2Good Guideline
    The words this page rests on
    Best Practice Advice 1: Serology is a crucial component of the detection and diagnosis of CD, particularly tissue transglutaminase-immunoglobulin A (TG2-IgA), IgA testing, and less frequently, endomysial IgA testing.
    Best Practice Advice 7: Reduction or avoidance of gluten before diagnostic testing is discouraged, as it may reduce the sensitivity of both serology and biopsy testing.
  13. Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome. Valent P, J Allergy Clin Immunol Pract, 2019. E2Good Consensus statement
    The words this page rests on
    In severe cases, an MCA syndrome (MCAS) may be diagnosed. However, overt MCAS is an unusual condition, and many patients referred because of suspected MCAS are diagnosed with other diseases (autoimmune, neoplastic, or infectious) unrelated to MCA or suffer from MCA-related (eg, allergic) disorders and/or comorbidities without fulfilling criteria of an overt MCAS.