Utility of Ara h 2 sIgE levels to predict peanut allergy in Canadian children

Systematic review and meta-analyses on the accuracy of diagnostic tests for IgE-mediated food allergy

The European Academy of Allergy and Clinical Immunology (EAACI) is updating the Guidelines on Food Allergy Diagnosis. We aimed to undertake a systematic review of the literature with meta-analyses to assess the accuracy of diagnostic tests for IgE-mediated food allergy. We searched three databases (Cochrane CENTRAL (Trials), MEDLINE (OVID) and Embase (OVID)) for diagnostic test accuracy studies published between 1 October 2012 and 30 June 2021 according to a previously published protocol (CRD42021259186). We independently screened abstracts, extracted data from full texts and assessed risk of bias with QUADRAS 2 tool in duplicate. Meta-analyses were undertaken for food-test combinations for which three or more studies were available. A total of 149 studies comprising 24,489 patients met the inclusion criteria and they were generally heterogeneous. 60.4% of studies were in children ≤12 years of age, 54.3% were undertaken in Europe, ≥95% were conducted in a specialized paediatric or allergy clinical setting and all included oral food challenge in at least a percentage of enrolled patients, in 21.5% double-blind placebo-controlled food challenges. 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. The basophil activation test (BAT) was highly specific for the diagnosis of peanut (90%) and sesame (93%) allergies. 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.

Safety of Multifood Oral Immunotherapy in Children Aged 1 to 18 Years at an Academic Pediatric Clinic

BACKGROUND

Oral immunotherapy (OIT) aims to increase the reaction threshold to a food allergen and decrease the risk of a potentially life-threatening allergic reaction in the event of an accidental ingestion. Whereas single-food OIT is the most extensively studied, data on multifood OIT are limited.

OBJECTIVE

Our study aimed to examine the safety and feasibility of single-food and multifood immunotherapy in a large cohort in an outpatient pediatric allergy clinic setting.

METHODS

A retrospective review of patients enrolled in single-food and multifood OIT between September 1, 2019, and September 30, 2020, and data collection of those patients until November 19, 2021, were performed.

RESULTS

There were 151 patients who underwent either an initial dose escalation (IDE) or a standard oral food challenge. Seventy-eight patients were receiving single-food OIT with 67.9% reaching maintenance. Fifty patients were undergoing multifood OIT with 86% reaching maintenance to at least 1 OIT food and 68% reaching maintenance for all their foods. Of the 229 IDEs, there were low frequencies of failed IDEs (10.9%), epinephrine administration (8.7%), emergency department referrals (0.4%), and hospital admission (0.4%). Cashew accounted for one-third of failed IDEs. Epinephrine administration during home dosing occurred in 8.6% of patients. Eleven patients discontinued OIT owing to symptoms during up-dosing. No patients discontinued once reaching maintenance.

CONCLUSIONS

Desensitization to 1 food or multiple foods simultaneously through OIT appears to be safe and feasible using the OIT protocol that has been established. The most common adverse reaction causing discontinuation of OIT was gastrointestinal symptoms.

Evolving Interpretation of Screening and Diagnostic Tests in Allergy

Diagnostic tests for allergy usually are performed to confirm a diagnosis of an allergic disease. If a food allergy suspected, a test can help to determine whether it is present, to monitor its activity over time, and to determine whether the allergy is resolving. In this way, tests are used for diagnosis, monitoring, screening, and prognosis. There are 2 schools of thought for using tests: Frequentist and Bayesian approaches. The Frequentist approach defines probability in terms of the frequency of an event if it were to be repeated numerous times and uses parameters such as sensitivity, specificity, and predictive values to make a diagnosis. In contrast, the Bayesian approach defines probability as the degree of belief or disbelief regarding the diagnosis and asserts that only data are real and that test parameters are to be inferred from the data. There are strengths and limitations to each approach; however, the Bayesian approach provides an algorithm leading to a disease probability. To use the Bayesian approach, test results need to be expressed as a likelihood ratio. This helps to determine how much the result of a test changes the probability of a particular diagnosis. Once a probability of disease is determined, decision thresholds need to be defined so that a treatment decision can be made. Using this Bayesian approach, the concept of a false-positive or false-negative test result becomes obsolete.

Peanut components measured by ISAC: comparison with ImmunoCap and clinical relevance in peanut allergic children

Background

Specific IgE (sIgE) against the peanut component Arachis hypogaea (Ara h) 2 has been shown to be the most important allergen to discriminate between peanut allergy and peanut tolerance. Several studies determined sIgE cut off values for Ara h 2, determined by singleplex measurements. However, cut off values for Ara h 2 from multiplex arrays are less well defined. The aim of this study was to evaluate the correlation between Ara h 2 sIgE determined by singleplex versus multiplex measurements and to assess the diagnostic value of the different peanut components included in Immuno Solid-phase Allergen Chip (ISAC) multiplex analysis in children with a suspected peanut allergy.

Methods

In this retrospective study we analyzed Ara h 2 sIgE values with singleplex Fluorescence Enzyme Immunoassay (FEIA, ImmunoCap) and multiplex microarray (ISAC) measurements in 117 children with a suspected peanut allergy. Also, other peanut components measured by ISAC were analyzed. Double blinded placebo controlled oral food challenges were used as golden standard.

Results

Among all studied peanut components FEIA Ara h 2 sIgE showed the highest area under the curve (AUC, 0.922), followed by ISAC Ara h 6 and Ara h 2 sIgE with AUCs of respectively 0.906 and 0.902. Best cut off values to diagnose peanut allergy were 4.40 kU/l for FEIA Ara h 2 sIgE and, 7.43 ISU and 8.13 ISU for respectively Ara h 2 and Ara h 6 sIgE in ISAC microarray. Ara h 2 sIgE determined in FEIA and ISAC showed a good correlation (r = 0.88; p < 0.01).

Conclusion

Ara h 6 and Ara h 2 sIgE in multiplex ISAC are both good predictors of clinical peanut allergy in Dutch children, and their performance is comparable to the use of Ara h 2 in singleplex FEIA. The simultaneous measurement of different peanut components using ISAC is an advantage and clinically useful to detect peanut allergic children that are Ara h 2 negative but sensitized to other peanut proteins such as Ara h 6.

Diagnostic accuracy of Ara h 2 for detecting peanut allergy in children

Background

Specific IgE to Ara h 2 is a diagnostic test for peanut allergy which may reduce the need for double‐blind placebo‐controlled food challenges (DBPCFC); however, guidance for using Ara h 2 in place of DBPCFCs has not been validated.

Objective

To prospectively evaluate 1) diagnostic accuracy of previously published Ara h 2 cut‐off levels to diagnose peanut allergy in children and 2) costs.

Methods

A consecutive series of 150 children age 3.5 to 18 years was evaluated in secondary and tertiary settings in the Netherlands. sIgE to Ara h 2 was the index test, and oral peanut ingestion was the reference test. Oral peanut ingestion was home or supervised introduction for Ara h 2 ≤ 0.1, DBPCFC for 0.1–5.0 and open food challenge for ≥5.0. Costs were calculated using financial healthcare data.

Results

A conclusive reference test was performed in 113 children (75%). Sixty‐four children (57%) had peanut allergy, as confirmed by a DBPCFC (27/47) or an open challenge (37/50). Forty‐nine children (43%) were considered peanut‐tolerant after peanut introduction (19/19), a DBPCFC (20/47) or an open challenge (10/50). Area under the curve for Ara h 2 was 0.94 (95% CI 0.90–0.98). The diagnostic flow chart correctly classified 26/26 (100%; 84–100) of children with Ara h 2 ≤ 0.1 as peanut‐tolerant and 34/35 (97%; 83–100) of children with Ara h 2 ≥ 5.0 as peanut‐allergic. At a cut‐off of ≤0.1 and ≥5.0, a sensitivity of respectively 100% (93–100) and 53% (38–67) was observed and a specificity of 53% (38–67) and 98% (87–100). Mean annual costs of the flow chart were estimated as €320‐€636 per patient lower than following national allergy guidelines.

Conclusions

In this diagnostic accuracy study, which did not take into account pretest probability, we have validated previously published Ara h 2 cut‐off levels which are associated with peanut tolerance and allergy.

Peanut allergy diagnosis: A 2020 practice parameter update, systematic review, and GRADE analysis

Given the burden of disease and the consequences of a diagnosis of peanut allergy, it is important that peanut allergy be accurately diagnosed so that an appropriate treatment plan can be developed. However, a test that indicates there is peanut sensitization present (eg, a "positive" test) is not always associated with clinical reactivity. This practice parameter addresses the diagnosis of IgE-mediated peanut allergy, both in children and adults, as pertaining to 3 fundamental questions, and based on the systematic reviews and meta-analyses, makes recommendations for the clinician who is evaluating a patient for peanut allergy. These questions relate to when diagnostic tests should be completed, which diagnostic tests to utilize, and the utility (or lack thereof) of diagnostic testing to predict the severity of a future allergic reaction to peanut.

Accuracy of component-resolved diagnostics in peanut allergy: Systematic literature review and meta-analysis

BACKGROUND

Peanut allergy diagnosis relies on clinical reactivity to peanut supported by detection of specific IgE (sIgE) antibodies. Extract-based sIgE tests have low specificity, so component-resolved diagnostics may complement whole-extract testing.

METHODS

We systematically collected peanut allergen component data in seven databases and studied the diagnostic accuracy of peanut storage proteins (Arah1, 2, 3) and cross-reactive peanut proteins (Arah8 PR-10 and Arah9 lipid transfer protein) through meta-analyses. The systematic literature review included studies employing peanut components and oral food challenge (OFC) as reference standard in patients suspected of peanut allergy. Data for component sIgE at pre-defined detection thresholds were extracted and combined in random-effects bivariate meta-analyses. Risk of bias was assessed as recommended by Cochrane, with two additional quality items of importance for this review.

RESULTS

Nineteen eligible studies presented data suitable for meta-analysis. In cross-sectional pediatric studies, the pooled sensitivity of Arah2-sIgE at 0.35 kU_A /L cutoff was 83.3% [95% CI 75.6, 88.9] and specificity in diagnosing objective peanut allergy was 83.6% [95% CI 77.4, 88.4]. Compared with 0.1 and 1.0 kU_A /L, this threshold provided the best diagnostic accuracy. At 0.35 kU_A /L, Arah1 and Arah3 had comparable specificity (86.0% and 88.0%, respectively) but significantly lower sensitivity compared with Arah2 (37.0% and 39.1%, respectively; P < .05).

CONCLUSION

sIgE to Arah2 can enhance the certainty of diagnosis and reduce the number of OFC necessary to rule out clinical peanut allergy in unclear cases.

Food allergy: A review and update on epidemiology, pathogenesis, diagnosis, prevention, and management

This review provides general information to serve as a primer for those embarking on understanding food allergy and also details advances and updates in epidemiology, pathogenesis, diagnosis, and treatment that have occurred over the 4 years since our last comprehensive review. Although firm prevalence data are lacking, there is a strong impression that food allergy has increased, and rates as high as approximately 10% have been documented. Genetic, epigenetic, and environmental risk factors are being elucidated increasingly, creating potential for improved prevention and treatment strategies targeted to those at risk. Insights on pathophysiology reveal a complex interplay of the epithelial barrier, mucosal and systemic immune response, route of exposure, and microbiome among other influences resulting in allergy or tolerance. The diagnosis of food allergy is largely reliant on medical history, tests for sensitization, and oral food challenges, but emerging use of component-resolved diagnostics is improving diagnostic accuracy. Additional novel diagnostics, such as basophil activation tests, determination of epitope binding, DNA methylation signatures, and bioinformatics approaches, will further change the landscape. A number of prevention strategies are under investigation, but early introduction of peanut has been advised as a public health measure based on existing data. Management remains largely based on allergen avoidance, but a panoply of promising treatment strategies are in phase 2 and 3 studies, providing immense hope that better treatment will be imminently and widely available, whereas numerous additional promising treatments are in the preclinical and clinical pipeline.