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.