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Home / Allergy and immune care / Testing
For clinicians

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.

8 minute read, written for clinicians14 sources, each checked word for wordLibrary checked October 20, 2026

Blood collection tubes with colored caps standing in a rack

This is the clinician view. It keeps every sentence of the plain guide and adds, for each section, the study design and citations of its sources, exact figures, and label wording quoted whole, marked For clinicians. Every added sentence is cited and checked like the rest. Back to plain language.

In short

How sure each claim is:E1StrongE2GoodOfficial textReviewWhat the grades meanUnderlined words open a definition

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

For clinicians

The work group report on oral food challenges details age-specific portion sizes, timing of antihistamine discontinuation, interpretation of serum and skin test results, written consents and instructional handouts.E2Good4

The evidence in this section (2 sources)
SourceDesignGradeCitations (NIH iCite)
1 Santos AF, Allergy, 2023GuidelineE2Good265 (RCR 42.15)
4 Bird JA, J Allergy Clin Immunol Pract, 2020Consensus statementE2Good196 (RCR 14.69)

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

For clinicians

The NIAID expert panel on skin and blood tests, quoted as written:

A positive SPT simply correlates with the presence of sIgE bound to the surface of cutaneous mast cells. Although the larger the mean wheal diameter provoked, the more likely that a food allergen will be of clinical relevance, the SPT alone is not diagnostic of FA.

A positive SPT or sIgE test result is indicative of allergic sensitization, but these findings alone may or may not be clinically relevant.

Quoted word for word from Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel (full text) E2Good8

Riggioni's 2024 meta-analysis found high sensitivity for skin prick tests with fresh cow's milk (90%) and raw egg (94%) in diagnosing milk and cooked egg allergy.E1Strong6

In Sampson's prospective study, more than 95% of food allergies were correctly identified by quantifying food-specific IgE against the previously established 95% predictive decision points for egg, milk, peanut and fish.E2Good7

The evidence in this section (5 sources)
SourceDesignGradeCitations (NIH iCite)
2 Nicolaou N, J Allergy Clin Immunol, 2010Observational studyE2Good325 (RCR 10.99)
5 Stiefel G, Clin Exp Allergy, 2017GuidelineE2Good101 (RCR 5.29)
6 Riggioni C, Allergy, 2024Meta-analysisE1Strong113 (RCR 25.52)
7 Sampson HA, J Allergy Clin Immunol, 2001Observational studyE2Good1,024 (RCR 32.23)
8 Boyce JA, 2010GuidelineE2GoodNot tracked

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.E2Good9

For clinicians

Component sIgE was highly specific in the same meta-analysis: Ara h 2 92% for peanut, Cor a 14 95% for hazelnut, Ana o 3 94% for cashew, casein 93% for cow's milk, and ovomucoid 92% and 91% for raw and cooked egg.E1Strong6

British guidelines describe pollen food syndrome as a distinct, usually mild disorder with oral and pharyngeal symptoms in people with hay fever or pollen sensitization. It can be triggered by nuts and can usually be told apart clinically from primary nut allergy.E2Good5

The evidence in this section (5 sources)
SourceDesignGradeCitations (NIH iCite)
1 Santos AF, Allergy, 2023GuidelineE2Good265 (RCR 42.15)
2 Nicolaou N, J Allergy Clin Immunol, 2010Observational studyE2Good325 (RCR 10.99)
9 Matsuo H, Allergy, 2008Observational studyE2Good120 (RCR 4.15)
6 Riggioni C, Allergy, 2024Meta-analysisE1Strong113 (RCR 25.52)
5 Stiefel G, Clin Exp Allergy, 2017GuidelineE2Good101 (RCR 5.29)

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.E2Good10

For clinicians

The EAACI task force's conclusion, quoted as written:

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.

Quoted word for word from Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report E2Good3
The evidence in this section (2 sources)
SourceDesignGradeCitations (NIH iCite)
3 Stapel SO, Allergy, 2008Consensus statementE2GoodNot tracked
10 Dykewicz MS, J Allergy Clin Immunol, 2020Practice parameterE2GoodNot tracked

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.E2Good11,12

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.E2Good13

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.E2Good14

For clinicians

AGA best practice advice: TG2-IgA at high levels (more than 10 times the upper limit of normal) is a reliable and accurate test for active celiac disease. Combined with a positive endomysial antibody in a second blood sample, its positive predictive value is virtually 100%.E2Good13

Valent and colleagues note that symptoms are sometimes misinterpreted as mast cell activation while other clinically relevant conditions are not thoroughly pursued. The two principal diagnoses that may underlie MCAS are severe allergy and systemic mastocytosis with severe mast cell activation.E2Good14

The evidence in this section (4 sources)
SourceDesignGradeCitations (NIH iCite)
11 Golden DBK, Ann Allergy Asthma Immunol, 2024Practice parameterE2Good282 (RCR 80.34)
12 Muraro A, Allergy, 2022GuidelineE2Good415 (RCR 48.27)
13 Husby S, Gastroenterology, 2019GuidelineE2Good176 (RCR 9.61)
14 Valent P, J Allergy Clin Immunol Pract, 2019Consensus statementE2Good157 (RCR 8.51)

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 GuidelinePMID 37815205; DOI 10.1111/all.15902; cited 265 times, relative citation ratio 42.15 (NIH iCite, 2026-10-16)
    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 studyPMID 20109746; DOI 10.1016/j.jaci.2009.10.008; cited 325 times, relative citation ratio 10.99 (NIH iCite, 2026-10-16)
    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 statementPMID 18489614
    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 statementPMID 31950914; DOI 10.1016/j.jaip.2019.09.029; cited 196 times, relative citation ratio 14.69 (NIH iCite, 2026-10-16)
    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.
    Tables and figures within the report and an extensive online appendix detail age-specific portion sizes, appropriate timing for antihistamine discontinuation, serum and skin test result interpretation, written consents, and instructional handouts that may be used in clinical practice.
  5. BSACI guideline for the diagnosis and management of peanut and tree nut allergy. Stiefel G, Clin Exp Allergy, 2017. E2Good GuidelinePMID 28836701; DOI 10.1111/cea.12957; cited 101 times, relative citation ratio 5.29 (NIH iCite, 2026-10-16)
    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.
    Pollen food syndrome is a distinct disorder, usually mild, with oral/pharyngeal symptoms, in the context of hay fever or pollen sensitisation, which can be triggered by nuts. It can usually be distinguish clinically from primary nut allergy.
  6. Systematic review and meta-analyses on the accuracy of diagnostic tests for IgE-mediated food allergy. Riggioni C, Allergy, 2024. E1Strong Meta-analysisPMID 38009299; DOI 10.1111/all.15939; cited 113 times, relative citation ratio 25.52 (NIH iCite, 2026-10-16)
    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.
    Skin prick test (SPT) with fresh cow's milk and raw egg had high sensitivity (90% and 94%) for milk and cooked egg allergies.
    Specific IgE (sIgE) to individual components had high specificity: Ara h 2-sIgE had 92%, Cor a 14-sIgE 95%, Ana o 3-sIgE 94%, casein-sIgE 93%, ovomucoid-sIgE 92/91% for the diagnosis of peanut, hazelnut, cashew, cow's milk and raw/cooked egg allergies, respectively.
  7. Utility of food-specific IgE concentrations in predicting symptomatic food allergy. Sampson HA, J Allergy Clin Immunol, 2001. E2Good Observational studyPMID 11344358; DOI 10.1067/mai.2001.114708; cited 1,024 times, relative citation ratio 32.23 (NIH iCite, 2026-10-16)
    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.
    On the basis of the previously established 95% predictive decision points for egg, milk, peanut, and fish allergy, greater than 95% of food allergies diagnosed in this prospective study were correctly identified by quantifying serum food-specific IgE concentrations.
  8. Guidelines for the Diagnosis and Management of Food Allergy in the United States: Report of the NIAID-Sponsored Expert Panel (full text). Boyce JA, 2010. E2Good Guideline
    The words this page rests on
    A positive SPT simply correlates with the presence of sIgE bound to the surface of cutaneous mast cells. Although the larger the mean wheal diameter provoked, the more likely that a food allergen will be of clinical relevance, the SPT alone is not diagnostic of FA.
    A positive SPT or sIgE test result is indicative of allergic sensitization, but these findings alone may or may not be clinically relevant.
  9. 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 studyPMID 18186814; DOI 10.1111/j.1398-9995.2007.01504.x; cited 120 times, relative citation ratio 4.15 (NIH iCite, 2026-10-16)
    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.
  10. Rhinitis 2020: A practice parameter update. Dykewicz MS, J Allergy Clin Immunol, 2020. E2Good Practice parameterPMID 32707227
    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.
  11. Anaphylaxis: A 2023 practice parameter update. Golden DBK, Ann Allergy Asthma Immunol, 2024. E2Good Practice parameterPMID 38108678; DOI 10.1016/j.anai.2023.09.015; cited 282 times, relative citation ratio 80.34 (NIH iCite, 2026-10-16)
    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.
  12. EAACI guidelines: Anaphylaxis (2021 update). Muraro A, Allergy, 2022. E2Good GuidelinePMID 34343358; DOI 10.1111/all.15032; cited 415 times, relative citation ratio 48.27 (NIH iCite, 2026-10-16)
    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.
  13. 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 GuidelinePMID 30578783; DOI 10.1053/j.gastro.2018.12.010; cited 176 times, relative citation ratio 9.61 (NIH iCite, 2026-10-16)
    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.
    Best Practice Advice 2a: TG2-IgA, at high levels (> ×10 upper normal limit) is a reliable and accurate test for diagnosing active CD. When such a strongly positive TG2-IgA is combined with a positive endomysial antibody in a second blood sample, the positive predictive value for CD is virtually 100%.
  14. Proposed Diagnostic Algorithm for Patients with Suspected Mast Cell Activation Syndrome. Valent P, J Allergy Clin Immunol Pract, 2019. E2Good Consensus statementPMID 30737190; DOI 10.1016/j.jaip.2019.01.006; cited 157 times, relative citation ratio 8.51 (NIH iCite, 2026-10-16)
    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.
    In fact, in several instances, symptoms are misinterpreted as MCA/MCAS, and other clinically relevant conditions are not thoroughly pursued.
    In addition, the algorithm proposed should help guide the investigating care providers to consider the 2 principal diagnoses that may underlie MCAS, namely, severe allergy and systemic mastocytosis accompanied by severe MCA.