Trophallergen Prick Tests (PT) : 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.