Food Allergies

Learning objectives

By the end of this chapter, participants will be able to:

• describe the diagnostic pathway for food allergy
• describe conventional and novel allergen sensitisation tests used to support the diagnosis of food allergy
• explain the potential uses component-resolved diagnostics can have in managing patients with food allergies in the clinic.

Food allergies

• Food allergies are defined as “adverse health effects arising from a specific immune response that occurs reproducibly on exposure to a given food”.¹
• They can be classified as:²

• Food can also cause non-IgE mediated immune reactions and non-immune reactions. The latter reactions are defined as food intolerances and can often be confused with food allergies.^1,3
• In Europe, primary food allergies are:
  • common – 7 million Europeans live with a food allergy⁴
  • increasing in prevalence⁵
  • mostly caused by peanuts, tree nuts, fish, shellfish, egg, milk, wheat and soy.⁶
• However, food allergies are often self-diagnosed and self-reported, causing prevalence rates to appear substantially higher than those confirmed with medical diagnostic tests.⁶

Clinical symptoms related to food allergies⁷

• Common symptoms associated with food allergies:

Why is a correct diagnosis important?

• Food allergies can cause anaphylaxis and be fatal to the patient.⁸
• To prevent unnecessary dietary restrictions that carry social, psychological and nutrition consequences.^9,10
• To identify IgE-mediated food allergies as food can cause both IgE- and non-IgE-mediated reactions.
  • These can share similar clinical symptoms such as eczematous rash/lesions, diarrhoea and pain.¹¹
• Food allergies are related to other atopic diseases including allergic rhinitis, asthma and atopic dermatitis.¹²

What barriers do clinicians often encounter during food allergy diagnosis?

Testing in food allergy

• To determine whether a patient’s symptoms are caused by an allergic disease as opposed to other common sources, an allergen sensitisation test can be conducted.
• Skin prick testing and sIgE testing are recommended.¹⁴ However:
  • Skin prick testing depends on availability, training and risks, which often preclude use in primary care.¹⁵
  • In vitro tests (i.e. sIgE) have the advantage that they are readily available in primary care, staff do not need extra training to perform them and there is no risk to the patient from reactivity.¹⁵
• Oral food challenge (OFC) can be used in conjunction with a clinical history and identification of IgE sensitisation to support a diagnosis of food allergy.¹⁴
  • Though OFC is considered the gold standard of food allergy diagnosis, it is often not viable as it must be performed in a specialist setting with emergency or intensive care support immediately available.
• In recent years, the ability to identify allergens at a molecular level has vastly expanded understanding of the mechanism of food allergy, and molecular diagnosis (component-resolved diagnostics [CRD]) should be added to the existing armamentarium of diagnostic testing.¹⁶
  • There is growing evidence that the use of molecular diagnosis in combination with conventional sensitisation testing improves analytical and diagnostic performance and can lead to a reduction in the need for diagnostic OFC in selected cases.

When is it advisable to send a patient for an oral food challenge test?

Component-resolved diagnostics in food allergy

• A blood sample is acquired from the patient and analysed for specific IgE antibodies against food allergen component.
• These tests can be carried out in a various singleplex (one component per sample) or in a multiplex (100> components per sample).

• CRD can be used to:
  • provide a patient-specific profile¹⁷
  • help discriminate between primary, secondary and cross-reactive food allergies¹⁸
  • relate sensitisation patterns to clinical symptoms and treatment^19,20
  • increase diagnostic accuracy when used in conjunction with traditional diagnostic tests, which can potentially reduce the number of OFCs.²¹
• There is increasing interest in the use of CRD in directing personalised care, particularly in children and older people.²²
• The novel concept of “bottom-up” diagnosis, i.e. “from molecules to clinic”, that CRD offers provides a reliable diagnostic workup in shorter time than conventional testing.²²

What role can component-resolved diagnostics play when diagnosing a food allergy?

Key considerations when using CRD in food allergy

• The patient’s clinical history and symptoms should be used to select the most relevant food components.
  • This will ensure that interpretations are made in the context of the patient’s clinical history and reduce the probability of false positive results.¹⁵
• Similar to specific IgE blood tests and skin prick tests, a positive IgE test conducted using CRD does not imply that this allergen source is clinically relevant.^15,16
  • Such results are only relevant if corresponding symptoms are present.

Summary

• Accurate diagnosis of IgE-mediated allergy is important due to the risk of anaphylaxis and to prevent unnecessary dietary restrictions, which carry social, psychological and nutrition consequences.
• In vitro testing should be used in primary care to support diagnosis of IgE-mediated food allergy.
• CRD can help differentiate between primary and secondary allergens and reduce the need for OFC.

References

1. Boyce JA et al. Nutr Res. 2011;31(1):61–75.
2. Worm M et al. Allergo J Int. 2015; 24:256–93.
3. Sicherer SH, Sampson HA. J Allergy Clin Immunol. 2018;141(1):41–58.
4. European Academy of Allergy and Clinical Immunology. https://www.eaaci.org/documents/EAACI_Advocacy_Manifesto.pdf (accessed May 2019).
5. Loh W, Tang MLK. Int J Environ Res Public Health. 2018;15(9):2043.
6. Nwaru BI et al. Allergy. 2014;69(8):992–1007.
7. Akdis CA, Agache I. (Editors). Global Atlas of Allergy. 2014. Zurich: European Academy of Allergy and Clinical Immunology.
8. Bock SA et al. J Allergy Clin Immunol. 2001;107(1):191–3.
9. Christie L et al. J Am Diet Assoc 2002:102(11):1648–51.
10. Shemesh E et al. Pediatrics. 2013;131(1):e10–e17.
11. Waserman S et al. Allergy Asthma Clin Immunol. 2018;14(Suppl 2):55.
12. Boyce JA et a. J Allergy Clin Immunol. 2010;126(60): S1–58.
13. Royal College of Paediatrics and Child Health. https://www.rcpch.ac.uk/sites/default/files/Taking_an_Allergy_Focused_Clinical_History_-_Allergy_Care_Pathways_Project.pdf (accessed May 2018).
14. National Institute for Health and Care Excellence. https://cks.nice.org.uk/food-allergy#!scenario (accessed May 2019)
15. Portnoy JM. Mo Med. 2011 Sep-Oct; 108(5): 339–43.
16. Matricardi PM et al. (Editors). Molecular Allergology User’s Guide. 2016. Zurich: European Academy of Allergy and Clinical Immunology.
17. Valenta R et al. Clinical and Experimental Allergy. 1999;29(7):896–904.
18. Luengo O, Cardona V. Clin Transl Allergy. 2014;4:28.
19. Canonica GW et al. World Allergy Organ J. 2013;6(1):17.
20. National Institute for Health and Care Excellence. https://www.nice.org.uk/guidance/DG24/documents/diagnostics-assessment-report (accessed May 2019).
21. Dang TD et al. J Allergy Clin Immunol. 2012;129(4):1056–63.
22. Mothes-Luksch N et al. World Allergy Organ J. 2018;11(1):22.