FASC: Fish Allergy in Spanish Children - A Study of New Cases of Fish Allergy in Children and Adolescents

Fish allergy is a major cause of IgE-mediated food allergy in children and is associated with a wide spectrum of clinical manifestations, ranging from mild reactions to severe anaphylaxis. Current knowledge of pediatric fish allergy is limited by geographical differences in dietary habits, fish species consumed, and patterns of allergen sensitization. Although component-resolved diagnostics have improved the characterization of fish allergy, comprehensive multicenter studies in children remain scarce.

The FASC study is a prospective, multicenter, observational study conducted in Spain to characterize children and adolescents with newly diagnosed IgE-mediated fish allergy. Consecutive eligible patients will be recruited in participating pediatric allergy units using standardized diagnostic and data collection procedures. Clinical information, allergy history, skin testing, serum specific IgE measurements, and molecular sensitization profiles will be collected. When clinically indicated, oral food challenges will be performed according to international recommendations and routine clinical practice.

The study aims to describe clinical phenotypes, molecular sensitization patterns, disease severity, quality of life, and geographical variability across Spain. The findings are expected to improve the understanding of pediatric fish allergy, support the identification of clinically relevant sensitization profiles, and contribute to more accurate diagnosis and individualized patient management.

Inclusion criteria

• Children and adolescents aged 0 to 17 years (up to 18 years of age).
• First clinical episode compatible with IgE-mediated fish allergy.
• Evidence of allergic sensitization demonstrated by at least one of the following:
• Positive skin prick test (wheal diameter ≥3 mm compared with the negative control); or
• Serum specific IgE ≥0.35 kUA/L to at least one fish species or fish allergen component.
• Written informed consent obtained from the parent(s) or legal guardian(s), and assent from participants aged 12 years or older, when applicable.

Exclusion criteria

• Age ≥18 years.
• Non-IgE-mediated fish allergy (e.g., fish-induced FPIES).
• Severe dermographism, chronic urticaria, or severe atopic dermatitis preventing reliable interpretation of skin prick testing.
• Inability to complete the diagnostic procedures required by the study.
• Absence of informed consent or, when applicable, participant assent.