Phadia’s F204 test is used to detect blood levels of the IgE (antibodies) responsible for allergic reactions to trout. The trout allergy is caused by parvalbumin, a protein found in many other fish. People who are allergic to trout will usually be allergic to other fish (cod, halibut, sole, etc.) but, unless there is a true double allergy, they will not be allergic to shellfish and other seafood. The interpretation chart accompanying the result expresses the probability of an allergic reaction to trout (and possibly other fish), but not necessarily the severity of the reaction. Case history (symptoms, relation to meals, etc.) and clinical examination by the physician are essential for a reliable interpretation of the results.
A negative anti-trout IgE result (< 0.3 kU/L) indicates that trout is probably not responsible for the symptoms reported by the person, but it DOES NOT COMPLETELY RULE OUT THIS POSSIBILITY. Both negative and positive results must be interpreted in light of the case history. The double-blind oral food challenge remains the definitive technique for confirming a trout allergy. Unlike allergies to milk and egg whites, the hypersensitivity to trout and other fish often emerges in adulthood and tends to persist for life.