Original article Cross-reactivity to eel, eelpout and ocean pout in codfish-allergic patients Fish allergy is one of the most common food allergies especially among adults and can be significant in popu- lations where fish is a major component in the food. The clinical manifestations are ranging from local oral allergy syndrome over urticaria to anaphylaxis (1–3). Patients found allergic to one fish species have in many cases been advised to avoid all kinds of fish without further evaluation. In the literature reports of extensive clinical cross-reactivity between fish species are common (4). For instance has serological cross-reactivity between codfish and various other fish species been suggested by means of skin prick test (SPT), histamine release (HR), radio allergosorbent test (RAST) and immunoblotting by Hansen et al. (2). There have, however, lately been several reports of patients reacting to only one or a few species (5–8). Because of a possible introduction of fish species hitherto not much seen on the Scandinavian market and the inconsistency in the literature regarding the cross-reactivity between different kinds of fish we have evaluated the IgE-mediated cross-reactivity of ocean pout, eelpout and eel. Methods Patients Eighteen patients (aged 16–44 years, median 31) diagnosed with codfish allergy, according to the guidelines published by The European Academy of Allergy and Clinical Immunology (9, 10), were recruited. All had a positive SPT to codfish and were positive in double-blind placebo-controlled food challenge (DBPCFC), except where their case history indicated that they had suffered anaphylaxis or a very severe reaction upon ingestion. This study was approved by the local ethical committee (Den videnskabsetiske komite´ for Vejle og Fyns amter) and informed consent was obtained from the patients. Fishes and extracts Ocean Pout was purchased from Aqua Bounty Canada Inc. (St John’s NF, Canada) while codfish, eel and eelpout were bought locally. Fish allergy is one of the most common food allergies in both children and adults and patients with allergic reactions to one fish species have in many cases been given the advice to avoid all fish, without further evaluation. The possible common reactivity between different fish species is not well studied. Because of this and a possible exploitation of fish species hitherto not much used in the Scandinavian diet ocean pout, eelpout and eel were evaluated. We examined the serological and biological cross-reactivity of these species in double-blind chal- lenged-confirmed codfish-allergic patients using CAP, Maxisorp-radio allergo- sorbent test (RAST) inhibition, western blot, skin prick test (SPT) and histamine release (HR). All 18 codfish allergic patients had specific IgE to ocean pout, eelpout and eel determined by Maxisorp-RAST. All four fish species could induce basophil HR using blood from 16 of 18 patients and all patients tested reacted in SPT. This study demonstrates that patients with a verified clinical allergy to codfish in a high frequency express biological cross-reactivity to other fish species. By RAST inhibition this common reactivity was shown to be a true cross-reactivity. E. Sten 1 , T. K. Hansen 2 , P. Stahl Skov 1 , S. B. Andersen 3 , AM. Torp 3 , U. Bindslev-Jensen 2 , C. Bindslev-Jensen 2 , L. K. Poulsen 1 1 Allergy Clinic, National University Hospital, Copenhagen; 2 Department of Dermatology I, Allergy Center, Odense University Hospital, Odense; 3 Department of Agricultural Sciences, The Royal Veterinary and Agricultural University, Copenhagen, Denmark Key words: allergy; codfish; eel; eelpout; fish cross- reactivity; Gad c1; ocean pout. Eva Sten Allergy Clinic TTA 7542 National University Hospital Blegdamsvej 9 2100 Copenhagen Ø Denmark Accepted for publication 17 December 2003 Abbreviations: CPM, counts per minute; Ig, immunoglobulin; FCS, fetal calf serum; HR, histamine release; RAST, radio allergosorbent test; SPT, skin prick test. Allergy 2004: 59: 1173–1180 Printed in UK. All rights reserved Copyright Ó Blackwell Munksgaard 2004 ALLERGY DOI: 10.1111/j.1398-9995.2004.00497.x 1173