Cross-reactivity in cashew nut allergy.

BACKGROUND: Cashew nut allergy is increasing globally and may cause cross-allergic reactions to seed kernels from botanically related plants, including citrus. CASE PRESENTATION: A woman in her twenties with a known nut allergy developed anaphylaxis after consuming a sports drink containing citrus-derived pectin. Skin prick testing revealed reactions to the sports drink (6 mm), lemon seed (14 mm), citrus pectin (6 mm), cashew (16 mm) and pistachio (11 mm). Serum-specific IgE testing confirmed sensitisation to storage proteins in cashew and other nuts, including Ana o 3, Cor a 9, Cor a 14, Jug r 1 and Ara h 3. The patient tolerated citrus fruits but had experienced lipoedema on contact with sliced lemon seeds and mild reactions to factory-made jam. Avoidance of citrus seed kernels and added pectin was recommended. INTERPRETATION: This case illustrates a rare but clinically significant cross-allergy between cashew nuts, citrus seeds and citrus-derived pectin contaminated with citrus seed allergens. Clinicians should be aware of such cross-reactivity when evaluating unexplained severe allergic reactions in patients with cashew nut allergy.