Allergists take several steps to pinpoint the source of allergy symptoms. In addition to conducting tests during which skin is pricked or blood is drawn, allergists also conduct a detailed medical history when screening an individual for food allergy.
Skin-prick tests involve using extract from the suspected allergenic food in a device that dispenses a tiny amount during the prick. The blood-draw test involves measuring the amount of antibodies in the blood sample that recognize allergenic protein fragments called “epitopes.” When an antibody called “immunoglobulin E” (IgE) binds to epitopes, the food is recognized as foreign by the immune system, and an allergic reaction occurs.
In the case of peanuts, commercial skin-prick allergy tests use extracts prepared from raw peanuts. However, Agricultural Research Service researchers in New Orleans, Louisiana, have found that roasted peanuts bind higher levels of IgE than raw peanuts.
At the unit, ARS chemist Soheila Maleki led a team that prepared individual extracts from raw, roasted, or boiled peanut samples. The scientists also procured three commercial extracts derived from raw peanuts under unknown methods. The team included colleagues from Louisiana State University in Shreveport.
Each of the 6 extracts was used in skin-prick tests on 19 study volunteers who had shown symptoms of peanut allergy and 4 volunteers who could eat peanuts without any symptoms.
Each of the individually prepared laboratory extracts—raw, roasted, or boiled—led to both false positives and false negatives. False positives occurred in nonallergic patients, and false negatives occurred in allergic patients.
“None of the three custom-made extracts tested individually showed optimal diagnostic reliability in terms of patient sensitivity and specificity,” says Maleki. At least three of the volunteers with a history of severe reaction to peanuts had a variety of reactions (including one false negative) to one or more of the three commercial extracts tested.
Maleki and colleagues suggest that future testing include a mix of extracts from raw, boiled, and roasted peanuts to enhance diagnostic capability.
The study was published in Annals of Allergy, Asthma, and Immunology in December 2010.—By Rosalie Marion Bliss, Agricultural Research Service Information Staff.
"Casting a Wider Net To Detect Peanut Allergy" was published in the October 2013 issue of Agricultural Research magazine.