The value of component testing in the diagnosis and management of peanut allergy

In 2013, a study demonstrated that food allergies had increased in prevalence by 50 percent over a 12-year period.¹ And there’s one food allergy that caught the attention of the media and the general public over that same time frame—peanut allergy. The reasons for this are complex, but the statistics suggest a dramatic story: Peanut allergy is the number one cause of death related to food-induced anaphylaxis.² It develops early in life and is rarely outgrown.3 Peanut allergy is a growing public health problem. In 1999, peanut allergy was estimated to affect 0.4 percent of children and 0.7 percent of adults in the U.S., and by 2010, peanut allergy prevalence had increased to approximately two percent among children.³

These statistics are just some of the reasons that peanut allergy has been classified as a significant public health threat—one without any present treatment or cure.³ Our understanding of the phenomenon is growing every day, as evidenced by the revised American Academy of Pediatrics-endorsed guidelines that reversed earlier recommendations. Instead of delayed introduction of peanut, the 2017 guidelines now recommend early introduction at four to six months.³ However, if an infant is at high risk of developing peanut allergy, with a history of eczema or egg allergy, allergy testing is recommended prior to introduction.³ 

It’s possible that the rise in peanut allergy may be in part due to prior recommendations of delayed introduction.² Regardless of the causes, it is essential that patients and their caregivers receive an accurate diagnosis as peanut allergy can be life threatening. Healthcare providers such as I use clinical history and physical examination to make that diagnosis as accurate as possible.  

The impact of component testing

Specific IgE testing is a valuable tool for any healthcare provider to have in their diagnosis repertoire. It’s been shown that adding this testing to a differential diagnosis greatly increases the confidence in the diagnosis.^4,5 Additionally, the diagnostic technology is advancing every day, with peanut component testing available to help paint a clearer picture of precisely which peanut components people are sensitized to.  

One such recent innovation was the addition of several new peanut components to ImmunoCAP Specific IgE blood testing assays, including Ara h 1, Ara h 2, Ara h 3, Ara h 6, Ara h 8, and Ara h 9. The tests for Ara h 1, 2, 3, and 6 have the potential to help the healthcare provider and patient better understand the risk of the patient having a systemic reaction. That’s because these components are more likely to cause a systemic reaction in sensitized individuals.⁶ Ara h 8 and 9, on the other hand, are typically associated with only local reactions (such as an itchy mouth).  

So how does that translate to patient management? A common practice to determine if a patient is clinically allergic to peanut is an oral food challenge (OFC). Though this is standard practice in food allergy testing,⁷ it can be a major source of stress for patients and caregivers.

With the use of a peanut component blood test, a sensitization to Ara h 1, 2, 3, and/or 6 may rule out the need of an OFC, due to the heightened risk of systemic reaction. On the other hand, patients not sensitized to these components may be more at ease before beginning the challenge. This is just one example of how component blood testing can make a huge difference.

In addition, if a patient is sensitized to Ara h 8 (also found in birch tree) and/or a type of protein called profilin, these are cross reactive proteins. Sensitization to cross reactive proteins means the patient is at a low risk for a systemic reaction and may actually tolerate eating peanuts. Cross-reactive proteins are more widely distributed and may be shared between a wide range of allergen sources. For example, a patient with a primary allergy to birch pollen may also experience a mild and localized peanut reaction because one of the peanut proteins is structurally similar to the protein in birch pollen.

At the end of the day, this kind of specificity in testing can help get to the bottom of what might be causing someone’s allergy symptoms, and that is good news for healthcare providers and patients alike.

REFERENCES

1. Jackson K, et al. Trends in Allergic Conditions Among Children: United States, 1997-2011. National Center for Health Statistics Data Brief. 2013. Retrieved from https://www.cdc.gov/nchs/data/databriefs/db121.pdf
2. Du Toit G, et al. Randomized Trial of Peanut Consumption in Infants at Risk for Peanut Allergy. The New England Journal of Medicine 2015; 1-11.
3. Togias A, et al. Addendum Guidelines for the Prevention of peanut allergy in the United States: Report of the National institute of Allergy and Infectious Disease- sponsored expert panel. J Allergy Clin  Immunol 2017;139,1:29-36.  
4. Duran-Tauleria E, et al. The utility of specific immunoglobulin E measurements in primary care. Allergy. 2004;59 (Suppl 78):35-41.
5. Niggemann B, et al. Pediatric allergy diagnosis in primary care is improved by invitro allergen specific IgE testing. Pediatr Allergy Immunol. 2008;19:325-331.
6. Sastre, J. Molecular diagnosis in allergy. Clinical & Experimental Allergy. 2010; 2.
7. Boyce JA, et al. Guidelines for the Diagnosis and Management of Food Allergy in the U.S.: Summary of the NIAID-Sponsored Expert Panel Report. J Allergy Clin Immunol 2010;126:1105-18.