Diagnostic value of peanut component testing in Australian children
Published: September 14, 2020
Peanut allergy affects 2-3% of Australian children, and in this population it is the most common cause of hospital presentations for anaphylaxis and of anaphylaxis related fatalities. Blood tests which measure levels of IgE production against some important peanut components (Ara h proteins) are widely used in clinical practice worldwide to guide diagnosis and to monitor for tolerance; however, their utility to accurately predict clinical peanut allergy, based upon a medically supervised oral food challenge, in Australian children, has not been established outside of their predictive capacity in infants.
In a recent article published by The Journal of Allergy and Clinical Immunology: In Practice, Kaur et al. report on outcomes of a study which examined whether IgE directed against Ara h protein components (Ara h 1, 2, 3, 6, 8, and 9) of children avoiding dietary peanut, who were referred for medically supervised oral food challenge to peanut to confirm, rule out and/or assess for tolerance, was useful in predicting clinical peanut allergy and/or severity of the allergic reaction at food challenge. Children (n – 222) referred by their allergists for medically supervised peanut challenge from 3 specialist allergy services in Sydney, Australia were recruited from The Children’s Hospital at Westmead, Sydney Children’s Hospital at Randwick and Campbelltown Hospital. Blood samples were collected from patients prior to peanut challenge and assayed for IgE to whole peanut and peanut components Ara h 1, 2, 3, 6, 8 and 9.
Of the 222 children, 83 (37%) had no history of prior peanut exposure and were avoiding peanut based on sensitization alone, 139 (63%) had a past history of clinical reaction to peanut, of which 32 had prior anaphylaxis to peanut. Of these 222, 133 (60%) were tolerant and 89 (40%) developed allergic symptoms during the challenge. One third (30/89) of these allergic children experienced anaphylaxis at peanut challenge, requiring treatment with epinephrine, while the remainder had mild/moderate allergic symptoms.
The authors reported that size of the peanut skin prick (SPT) wheal, level of total peanut IgE and IgE specific to Ara h 2 performed similarly to predict children who reacted on challenge (area under the curve; 0.84-0.87). However, all children (n=11) who had levels of IgE to all 3 of Ara h 1, 2 and 3 above 0.35 kUA/L reacted on peanut challenge, with 7 experiencing anaphylaxis. Moreover, overall severity of reaction and lower peanut eliciting dose were correlated with level of polysensitization to Ara h 1, 2 and 3. IgE to Ara h 8 and 9 were not useful in predicting challenge outcomes in this cohort.
Overall, the authors concluded that testing for all 3 of Ara h 1, 2 and 3 in children with a relatively low pre-test probability of ongoing peanut allergy may provide higher utility than single components, SPT or total peanut IgE alone. In this cohort, children with sensitization to all three of Ara h 1, 2 and 3 were very likely to be clinically allergic. This information may assist in informing whether to proceed with a peanut challenge and may avoid unnecessary peanut challenges, which are time consuming and resource intensive and may result in anaphylaxis.
The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.