D1.207 - “Do nut know what: What is the current role of the prick test and serum IgE in the diagnosis of walnut allergy?

Nuts are a common trigger of IgE-mediated FA (Food Allergy). Diagnosis relies on clinical history, skin prick test (SPT), s-IgE (serum IgE), BAT (basophil activation test) and OFC (Oral Food Challenge). The PV (predictive value) of sIgE varies according to the population and the specific allergen. Jugr1 has high specificity in the diagnosis of FA, Jugr3 seems to be prevalent in Italian patients.

Description of two cases of anaphylaxis following a challenge, with prick test and IgE levels showing extremely different results.

The first is a textbook case of an allergic 8-year-old boy who developed anaphylaxis. The boy was polysensitized to nuts and airborne allergens and had a previous OAS (Oral Allergy Syndrome) after tree nut ingestion, with spontaneous regression. Prick by prick (PBP) was positive for walnut (6 mm) with total IgE 1058 kUA/l, specific IgE for walnut 6,94 kUA/l, Jugr1 5.02 kUA/l, Jugr3 3.16 kUA/l. OFC was performed to confirm walnut FA. He developed anaphylaxis with cutaneous, pulmonary and gastrointestinal involvement after ingestion of 13.7g of walnut, with resolution within two hours following the administration of cetirizine, salbutamol and prednisone, without the need for adrenaline. The second case showed an unexpected result. Another 8-year-old child polysensitized to walnut, hazelnut and airborne allergens presented ocular symptoms and OAS after tree nut ingestion. PbP test was positive for walnut (4 mm), total IgE were 25 kUA/l, specific IgE for walnut 0,17 kUA/l, Jugr1 and Jugr3 were negative. The extendend test (ALEX2) showed only positivity of Jugr1 0,20 kUA/l, therefore was less sensitive than individual molecular tests. The girl developed anaphylaxis with cutaneous and respiratory involvement after ingestion of 9.52g of walnut, requiring cetirizine, prednisone and intramuscular adrenaline for the resolution.

It’s difficult predicting tree nut FA severity based on sPT and specific s-IgE levels. In the literature, their PV is known to vary depending on the type of food tested and the patient’s polysensitization profile, as shown by the unexpected anaphylactic reaction in the second case. This makes the diagnostic utility of sPTS and specific IgE still a matter of debate. What value can the BAT have in avoiding the need for an OFC, which remains the gold standard for walnut allergy diagnosis?

References:

1.Chudoba A, Żebrowska A, Sybilski AJ. Tree Nut Allergy in Children-What Do We Know? -A Review. Nutrients. 2024; 16(23):3978.

2.Cela L, Gravina A, Semeraro A, et al. Oral Food Challenge in Children with Tree Nut and Peanut Allergy: The Predictive Value of Diagnostic Tests. Diagnostics (Basel). 2024; 14(18):2069.

3.Dramburg S, Hilger C, Santos AF, et al. EAACI Molecular Allergology User's Guide 2.0. Pediatr Allergy Immunol. 2023; 34 Suppl 28.

4.Matricardi PM. The Very Low IgE Producer: Allergology, Genetics, Immunodeficiencies, and Oncology. Biomedicines. 2023; 11(5):1378.