Trophallergen Prick Tests : Influence of Food Sample Shelf Life on the Reproducibility of PT Results

Prick tests (PT) are the standard skin tests used in the investigation of immediate IgE-mediated food allergies. Their use as a first-line tool in allergological investigations is strongly recommended by the European Academy of Allergy and Clinical Immunology (EAACI). These tests involve locally reproducing histamine release manifestations in the epidermis by superficially introducing an allergen to confirm or rule out its role in the onset of clinical symptoms compatible with an allergy. During the diagnostic management and follow-up of patients with food allergies, the technique used is the "prick to prick" method, due to the lack of reliable access to many standardized commercial food extracts. This method involves piercing the food with a sterile lancet (to deposit food content on its surface) and then making a superficial skin puncture with the same device on the anterior surface of the forearm to introduce a tiny fraction of the food and its proteins into the epidermis, where mast cells are present. Simultaneously, a positive control and a negative control are performed. The tests are read after 15 to 20 minutes by measuring the size in millimeters of the resulting papules and erythema. A PT for the tested allergen is considered positive if the average diameter of the resulting papule is 3 mm or more and/or at least half the size of the positive control papule. The procedure is well-tolerated, allowing it to be performed at any age, in both hospital and outpatient settings. The risk of a systemic reaction has been evaluated at 0.008%, with no severe reactions observed.

This method, performed with native foods (unprocessed food, uncontaminated foods), either raw or cooked (depending on the nature of the allergen being tested), is preferred over the use of commercial extracts (standardized commercial allergen preparations) due to its better sensitivity and specificity, the high cost of commercial extracts, and the lack of commercial extracts for certain foods. For practical reasons, given the wide variety of possible allergens, and to most accurately reproduce the exposure that caused the reaction, the most common approach is to ask the patient to bring their own foods for testing. These foods should be brought in a fresh state. However, situations where the patient is offered a food PT but does not have fresh native foods are common. Indeed, many patients forget to bring them. Similarly, during a consultation to explore a respiratory or drug allergy, the interview may lead to the detection of a food allergy that needs to be tested at the same time. Given the delays in allergology consultations, the severity of food allergy symptoms, and the potential risk of delayed diagnosis, all allergists involved in managing food allergies are led to create a library of food samples stored either in a dry state (e.g., nuts, peanuts, cereal flours) or frozen for perishable foods (meats, shellfish, fruits, vegetables). To our knowledge, after reviewing the literature, no guidelines for best practices regarding the storage of these food samples for PT purposes have been established by scientific societies. Moreover, while the impact of freezing and thawing methods on the denaturation of food proteins is known, the effect of freezing and its duration on the sensitivity and specificity of PT is poorly understood.

The objective of our study is to evaluate the reproducibility of PT results between those performed with fresh foods and those performed with preserved foods at different storage dates in participants who have experienced anaphylaxis of at least grade 2 according to the Ring and Messmer classification.

Interventional, exploratory, prospective, single-center clinical study comparing for each patient included, at the same time, the results of prick tests carried out with fresh native food allergens and those carried out with native foods stored for prolonged period (in the freezer or dry dependig on the nature of the product) and for different shelf lives.

A native food is a raw food not contaminated by other foods. It is said to be fresh if it has not been subject to a prolonged preservation technique such as freezing or canning. The native food can be raw or cooked depending on the nature of the food and the nature of the allergic protein tested.

In our study the patient is his own witness. Carrying out all tests in a single session makes it possible to avoid analysis biases related to intra-individual variabilities in reactivity encountered during prick tests carried out on different dates (patient included only once in the study, no re-inclusion possible). In our study, several foods can be tested for the same patient depending on the number of food allergies that the patient has.

The completion of the study does not change the follow up methods for patients who are already offered prick tests as part of their allergic pathology. The study lasts approximately 30 minutes for each patient, while the prick tests are carried out. Their follow up is carried out by nurses of the allergology department for 30 minutes from the completion of the prick tests and this, under the responsibility of the allergist doctor of the department whose presence is obligatory when performing these tests.

Participants will be fully and honestly informed, in understandable terms, about the objectives and constraints of the study, the potential risks incurred, the necessary monitoring and safety measures, and their rights to refuse to participate in the study or to withdraw at any time.

All this information is provided in an information form given to the patient. The patient's written consent will be obtained by the investigator, a junior doctor, or a representative doctor before any procedure specific to the study.

As this is a pilot, exploratory, monocentric study, and given that Orléans University Hospital receives approximately 50 patients per year (who meet the eligibility criteria), it is planned to include 100 patients in the study over a maximum period of 30 months.

A clinical research associate (ARC) mandated by the sponsor will ensure the proper conduct of the study, the collection of generated data, its documentation, recording, and reporting, in accordance with the Standard Operating Procedures implemented within Orléans University Hospital and in compliance with Good Clinical Practices as well as the applicable legislative and regulatory provisions.

Participants will be fully and honestly informed, in understandable terms, about the objectives and constraints of the study, the potential risks incurred, the necessary monitoring and safety measures, and their rights to refuse to participate in the study or to withdraw at any time.

All this information is provided in an information form given to the patient. The patient's written consent will be obtained by the investigator, a junior doctor, or a representative doctor before any procedure specific to the study.

Eligibility Criteria:
Inclusion Criteria:

1. Aged 18 and over.
2. Having a diagnosis of food allergy(ies) due to one or more of the food allergen studied, previously made by an allergologist, of grade 2 to 3 according to the Ring and Messmer classification.
3. Having given consent to participate in the study.

The diagnosis is made by the allergologist of the department due to the presence of a compatible clinical history implicating the tested allergen, the presence of evidence of sensitization to the allergen (positive prick-test and/or positive specific IgE assays), or even a positive oral allergen reintroduction test.

Exclusion Criteria:

1. Anaphylactic reaction dating less than 6 weeks
2. Hospitalization for asthma in the past 3 months
3. History of grade 4 anaphylactic reaction according to the Ring and Messmer classification.
4. Systemic antihistamine treatment in the 7 days preceding the test
5. Systemic beta-blocker treatment on the day of the test.
6. Protected person (under guardianship or curatorship)
7. Person under judicial supervision
8. Persons deprived of liberty
9. Person not affiliated with a social security insurance
10. Pregnant or breastfeeding women